Fix warnings about unhandled enum value in switch [-Wswitch]

Fixes GCC 5 warnings of the form:

core/io/http_client.cpp:288:9: warning: enumeration value 'STATUS_SSL_HANDSHAKE_ERROR' not handled in switch [-Wswitch]
core/io/marshalls.cpp:806:9: warning: enumeration value 'AABB' not handled in switch [-Wswitch]

Those can be trivial cases where adding a default fallback is the solution,
or more complex issues/hidden bugs where missed values are actually meant
to be handled.

editor/plugins/baked_lightmap_editor_plugin.cpp

@@ -50,6 +50,7 @@ void BakedLightmapEditorPlugin::_bake() {
 			case BakedLightmap::BAKE_ERROR_CANT_CREATE_IMAGE:
 				EditorNode::get_singleton()->show_warning(TTR("Failed creating lightmap images, make sure path is writable."));
 				break;
+			default: {}
 		}
 	}
 }