Merge pull request #2079 from manisandro/mutex

Add missing mutex lock

Author: mhugent

src/core/qgsconnectionpool.h

@@ -117,7 +117,9 @@ class QgsConnectionPoolGroup
         return 0;
       }
 
+      connMutex.lock();
       acquiredConns.append( c );
+      connMutex.unlock();
       return c;
     }