operator=, which was only used for clearing, wasn't clearing the hash.
This led to a mismatch between the vector and the hash (given that the hash
points into the vector).
Spotted by interrupting kmail in gdb, and it was in this code
iterating over a 2000 entries hash (the first vector entries not matching
the hash, this code keep appending new entries for the same formats).
This fixes QTBUG-8862 again, the initial fix having been accidentally
reverted in 467b15a.
Change-Id: Ia34b3d002a0199e1930431a4bbdb2ec981ed4ffc
Task-number: QTBUG-8862
Reviewed-by: Olivier Goffart (Woboq GmbH) <ogoffart@woboq.com>
90b48a70ff