Fix error when non-ASCII characters in resource pack path

(cherry picked from commit df5c68af99993002c927b4cc33bc85f67900579d)

core/io/file_access_zip.cpp

@@ -47,7 +47,7 @@ static void *godot_open(voidpf opaque, const char *p_fname, int mode) {
 		return nullptr;
 	}
 
-	Ref<FileAccess> f = FileAccess::open(p_fname, FileAccess::READ);
+	Ref<FileAccess> f = FileAccess::open(String::utf8(p_fname), FileAccess::READ);
 	ERR_FAIL_COND_V(f.is_null(), nullptr);
 
 	ZipData *zd = memnew(ZipData);