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.

core/io/resource_format_binary.h

@@ -127,7 +127,7 @@ class ResourceFormatSaverBinaryInstance {
 	bool skip_editor;
 	bool big_endian;
 	bool takeover_paths;
-	FileAccess *f;
+	FileAccess *f = nullptr;
 	String magic;
 	Set<RES> resource_set;