Utils: Allow storeFromVariant(QVariant())

This appears in reality.

Change-Id: Ib09a737a3378e26d88397dceb32a38c3857ec9b2
Reviewed-by: Christian Kandeler <christian.kandeler@qt.io>

src/libs/utils/store.cpp

@@ -31,6 +31,9 @@ Store storeFromVariant(const QVariant &value)
     if (value.typeId() == QMetaType::QVariantMap)
         return storeFromMap(value.toMap());
 
+    if (!value.isValid())
+        return {};
+
     QTC_CHECK(false);
     return Store();
 }