ideviceimagemounter: Fix possible memleak in option parsing
ideviceimagemounter: Fix possible memleak in option parsing

If some arguments are passed multiple times, don't leak the memory used
for the value of the first arguments passed.

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