Fix Coverity reports of uninitialized scalar variable

Fixes most current reports on Coverity Scan of uninitialized scalar
variable (CWE-457): https://cwe.mitre.org/data/definitions/457.html

These happen most of the time (in our code) when instanciating structs
without a constructor (or with an incomplete one), and later returning
the instance. This is sometimes intended though, as some parameters are
only used in some situations and should not be double-initialized for
performance reasons (e.g. `constant` in ShaderLanguage::Token).

editor/plugins/asset_library_editor_plugin.cpp

@@ -639,7 +639,7 @@ const char *EditorAssetLibrary::support_key[SUPPORT_MAX] = {
 
 void EditorAssetLibrary::_select_author(int p_id) {
 
-	//opemn author window
+	// Open author window
 }
 
 void EditorAssetLibrary::_select_category(int p_id) {
@@ -659,16 +659,6 @@ void EditorAssetLibrary::_select_category(int p_id) {
 void EditorAssetLibrary::_select_asset(int p_id) {
 
 	_api_request("asset/" + itos(p_id), REQUESTING_ASSET);
-
-	/*
-	if (description) {
-		memdelete(description);
-	}
-
-
-	description = memnew( EditorAssetLibraryItemDescription );
-	add_child(description);
-	description->popup_centered_minsize();*/
 }
 
 void EditorAssetLibrary::_image_update(bool use_cache, bool final, const PoolByteArray &p_data, int p_queue_id) {
@@ -774,7 +764,7 @@ void EditorAssetLibrary::_image_request_completed(int p_status, int p_code, cons
 		_image_update(p_code == HTTPClient::RESPONSE_NOT_MODIFIED, true, p_data, p_queue_id);
 
 	} else {
-		WARN_PRINTS("Error getting PNG file for asset id " + itos(image_queue[p_queue_id].asset_id));
+		WARN_PRINTS("Error getting PNG file from URL: " + image_queue[p_queue_id].image_url);
 		Object *obj = ObjectDB::get_instance(image_queue[p_queue_id].target);
 		if (obj) {
 			obj->call("set_image", image_queue[p_queue_id].image_type, image_queue[p_queue_id].image_index, get_icon("ErrorSign", "EditorIcons"));

editor/plugins/asset_library_editor_plugin.h

@@ -241,7 +241,6 @@ class EditorAssetLibrary : public PanelContainer {
 
 		bool active;
 		int queue_id;
-		int asset_id;
 		ImageType image_type;
 		int image_index;
 		String image_url;

editor/plugins/canvas_item_editor_plugin.cpp

@@ -628,7 +628,7 @@ void CanvasItemEditor::_save_canvas_item_state(List<CanvasItem *> p_canvas_items
 			if (bone && bone->has_meta("_edit_bone_")) {
 				// Check if we have an IK chain
 				List<Node2D *> bone_ik_list;
-				bool ik_found;
+				bool ik_found = false;
 				bone = Object::cast_to<Node2D>(bone->get_parent());
 				while (bone) {
 					bone_ik_list.push_back(bone);

editor/plugins/tile_map_editor_plugin.h

@@ -125,12 +125,11 @@ class TileMapEditor : public VBoxContainer {
 		bool yf;
 		bool tr;
 
-		CellOp() {
-			idx = -1;
-			xf = false;
-			yf = false;
-			tr = false;
-		}
+		CellOp() :
+				idx(TileMap::INVALID_CELL),
+				xf(false),
+				yf(false),
+				tr(false) {}
 	};
 
 	Map<Point2i, CellOp> paint_undo;
@@ -141,8 +140,12 @@ class TileMapEditor : public VBoxContainer {
 		bool flip_h;
 		bool flip_v;
 		bool transpose;
-		int auto_x;
-		int auto_y;
+
+		TileData() :
+				cell(TileMap::INVALID_CELL),
+				flip_h(false),
+				flip_v(false),
+				transpose(false) {}
 	};
 
 	List<TileData> copydata;

editor/plugins/tile_set_editor_plugin.cpp

@@ -805,7 +805,7 @@ void TileSetEditor::_on_workspace_input(const Ref<InputEvent> &p_ie) {
 							Vector2 coord((int)(mb->get_position().x / (spacing + size.x)), (int)(mb->get_position().y / (spacing + size.y)));
 							Vector2 pos(coord.x * (spacing + size.x), coord.y * (spacing + size.y));
 							pos = mb->get_position() - pos;
-							uint16_t bit;
+							uint16_t bit = 0;
 							if (tileset->autotile_get_bitmask_mode(get_current_tile()) == TileSet::BITMASK_2X2) {
 								if (pos.x < size.x / 2) {
 									if (pos.y < size.y / 2) {
@@ -868,7 +868,7 @@ void TileSetEditor::_on_workspace_input(const Ref<InputEvent> &p_ie) {
 						Vector2 coord((int)(mm->get_position().x / (spacing + size.x)), (int)(mm->get_position().y / (spacing + size.y)));
 						Vector2 pos(coord.x * (spacing + size.x), coord.y * (spacing + size.y));
 						pos = mm->get_position() - pos;
-						uint16_t bit;
+						uint16_t bit = 0;
 						if (tileset->autotile_get_bitmask_mode(get_current_tile()) == TileSet::BITMASK_2X2) {
 							if (pos.x < size.x / 2) {
 								if (pos.y < size.y / 2) {
@@ -1146,7 +1146,7 @@ void TileSetEditor::_on_tool_clicked(int p_tool) {
 				case EDITMODE_COLLISION: {
 					if (!edited_collision_shape.is_null()) {
 						Vector<TileSet::ShapeData> sd = tileset->tile_get_shapes(get_current_tile());
-						int index;
+						int index = -1;
 						for (int i = 0; i < sd.size(); i++) {
 							if (sd[i].shape == edited_collision_shape) {
 								index = i;