Fix integer overflow in Query Cache size #2040

lib/Query_Cache.cpp

@@ -403,7 +403,7 @@ void * Query_Cache::purgeHash_thread(void *) {
 	MySQL_Thread * mysql_thr = new MySQL_Thread();
 	MySQL_Monitor__thread_MySQL_Thread_Variables_version=GloMTH->get_global_version();
 	mysql_thr->refresh_variables();
-	max_memory_size=mysql_thread___query_cache_size_MB*1024*1024;
+	max_memory_size = (uint64_t) mysql_thread___query_cache_size_MB*1024*1024;
 	while (shutdown==0) {
 		usleep(purge_loop_time);
 		unsigned long long t=monotonic_time()/1000;
@@ -413,7 +413,7 @@ void * Query_Cache::purgeHash_thread(void *) {
 			if (MySQL_Monitor__thread_MySQL_Thread_Variables_version < glover ) {
 				MySQL_Monitor__thread_MySQL_Thread_Variables_version=glover;
 				mysql_thr->refresh_variables();
-				max_memory_size=mysql_thread___query_cache_size_MB*1024*1024;
+				max_memory_size = (uint64_t) mysql_thread___query_cache_size_MB*1024*1024;
 			}
 		}
 		unsigned int curr_pct=current_used_memory_pct();