Optimize SQL set creation.

src/QtLocationPlugin/QGCTileCacheWorker.cpp

@@ -454,6 +454,7 @@ QGCCacheWorker::_createTileSet(QGCMapTask *mtask)
             task->tileSet()->setId(setID);
             //-- Prepare Download List
             quint64 tileCount = 0;
+            _db->transaction();
             for(int z = task->tileSet()->minZoom(); z <= task->tileSet()->maxZoom(); z++) {
                 QGCTileSet set = QGCMapEngine::getTileCount(z,
                     task->tileSet()->topleftLon(), task->tileSet()->topleftLat(),
@@ -493,6 +494,7 @@ QGCCacheWorker::_createTileSet(QGCMapTask *mtask)
                     }
                 }
             }
+            _db->commit();
             //-- Done
             _updateSetTotals(task->tileSet());
             task->setTileSetSaved();