Zero initialize all pointer class and struct members

This prevents the pitfall of UB when checking if they have been
assigned something valid by comparing to nullptr.

modules/openxr/extensions/openxr_extension_wrapper.h

@@ -43,7 +43,7 @@ class OpenXRAPI;
 
 class OpenXRExtensionWrapper {
 protected:
-	OpenXRAPI *openxr_api;
+	OpenXRAPI *openxr_api = nullptr;
 
 	// Store extension we require.
 	// If bool pointer is a nullptr this means this extension is mandatory and initialisation will fail if it is not available