The terms db contains terms, where each terms is stored independently
(terminated with 0), or as a suffix to the previous term (terminated with
1).
In case of corrupted data, the first terminator seen may be a 1, which
leads to a crash when trying to access the previous term with
QVector<>::last().
Show a debug message, to give a hint about the bad data, which can be
fixed by reindexing the relevant file.
BUG: 392878
CCBUG: 392877