[iOS] Fix plugin configuration loading

Clear ConfigFile parameter before loading new file.
Ignore duplicate input plist keys

(cherry picked from commit aa321f0a244fd0a8c072806a12203b8de9b50135)

platform/iphone/plugin/godot_plugin_config.h

@@ -255,6 +255,8 @@ static inline PluginConfigIOS load_plugin_config(Ref<ConfigFile> config_file, co
 		return plugin_config;
 	}
 
+	config_file->clear();
+
 	Error err = config_file->load(path);
 
 	if (err != OK) {