Validate input in `ScriptServer::register_language`

core/object/script_language.cpp

@@ -166,6 +166,7 @@ ScriptLanguage *ScriptServer::get_language(int p_idx) {
 }
 
 void ScriptServer::register_language(ScriptLanguage *p_language) {
+	ERR_FAIL_NULL(p_language);
 	ERR_FAIL_COND(_language_count >= MAX_LANGUAGES);
 	_languages[_language_count++] = p_language;
 }