Fix crash in key lookup

std::sort expects a lambda returning a bool for whether the first element is smaller than the second one.
qstricmp returns an int in the strcmp style, which brings std::sort into an unpredictable state.

(cherry picked from commit 9b3730193ad13d93e6fded47340c9a1b13ad7718)

• GnuPG-Bug-ID: T7158