Just like any other container, it's legitimate for the user to
pass key/values belonging to the same container.
Q(Multi)Map::remove(Key) are already safe (either they call
erase() directly on std::(multi)map, where it does the right thing,
or they skip elements while detaching).
However, QMultiMap::remove(Key, T) wasn't safe in this regard
(the implementation is hand rolled), so take copies before start
erasing.
Change-Id: I87767d608b83216a6ff264fb6c8f145fdb5934f8
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>