Fix crash on populating style data to tabbar without parent

This resolves Bug 1966

src/styles/qcommonstyle.cpp

@@ -468,6 +468,7 @@ const QStyleControlElementData &populateControlElementDataFromWidget(const QWidg
 							ceData.tabBarData.identIndexMap[currentTab->identifier()] = tb->indexOf(currentTab->identifier());
 						}
 					}
+					if ( tb->parent() ) {
 						updateObjectTypeListIfNeeded(tb->parent());
 						if ((const_cast<QObject*>(tb->parent())->controlElementDataPrivateObject())->isQTabWidget) {
 							const QTabWidget *tw = static_cast<const QTabWidget*>(tb->parent());
@@ -507,6 +508,7 @@ const QStyleControlElementData &populateControlElementDataFromWidget(const QWidg
 						}
 					}
 				}
+			}
 			if (ceDataPrivate->isQToolBox) {
 				const QToolBox *tb = static_cast<const QToolBox*>(widget);
 				if (tb) {