Copy locale modifiers when creating XimInstCallback
Locale modifiers may be freed whenever XSetLocaleModifiers gets called, even if the locale hasn't changed. This means that we cannot save a pointer to those modifiers in the XimInstCallback record and must, instead, make a copy of them instead.
This fixes a problem uncovered when running wish under libasan as follows (on current Debian unstable):
$ LD_PRELOAD=/usr/lib/x86_64-linux-gnu/libasan.so.6 wish