Fix a bug in get_multiple_idle_connections() #3628

2.3.0 introduces a bug that prevents proxysql to run ping on backend
connections to keep them alive.

lib/MySQL_HostGroups_Manager.cpp

@@ -3548,8 +3548,22 @@ int MySQL_HostGroups_Manager::get_multiple_idle_connections(int _hid, unsigned l
 	drop_all_idle_connections();
 	int num_conn_current=0;
 	int j,k;
-	MyHGC* myhgc = MyHGC_find(_hid);
-	if (myhgc) {
+	MyHGC* myhgc = NULL;
+	for (int i=0; i<(int)MyHostGroups->len; i++) {
+		if (_hid == -1) {
+			// all hostgroups must be examined
+			// as of version 2.3.2 , this is always the case
+			myhgc=(MyHGC *)MyHostGroups->index(i);
+		} else {
+			// only one hostgroup is examined
+			// as of version 2.3.2 , this never happen
+			// but the code support this functionality
+			myhgc = MyHGC_find(_hid);
+			i = (int)MyHostGroups->len; // to exit from this "for" loop
+			if (myhgc == NULL)
+				continue; // immediately exit
+		}
+		if (_hid >= 0 && _hid!=(int)myhgc->hid) continue;
 		for (j=0; j<(int)myhgc->mysrvs->cnt(); j++) {
 			MySrvC *mysrvc=(MySrvC *)myhgc->mysrvs->servers->index(j);
 			//PtrArray *pa=mysrvc->ConnectionsFree->conns;