qt: fix cleanup of cache
reverts 018f4890
it was not that m_cachedData was deleted (see commit above) but the parent cache
itself was deleted after emitting a signal in its member function
fix: don't instantly clean up the cache in the source when requested since the requester can be the cache itself.
fixes empty label is not visible in any view
fixes model is always in a loading state
Edited by Prince Gupta