idevicescreenshot: Remove unnecessary math functions to find a unique filename
idevicescreenshot: Remove unnecessary math functions to find a unique filename

Removes repeated malloc/free too, limits the maximum filenames to try to 65535
and fails if no unique filename could be found. I think this limit is VERY
generous. If there are really so many files to test against it will also cause
an unconveniently long delay, but I felt a lower limit could still be easily
reached.

libimobiledevice-win32/libimobiledevice,libimobiledevice-win32/libimobiledevice,libimobiledevice-win32/libimobiledevice,libimobiledevice/libimobiledevice,libimobiledevice/libimobiledevice,libimobiledevice-win32/libimobiledevice