Reduce some unnecessary X calls.

Reduce some unnecessary X calls.

* src/xfns.c (x_real_pos_and_offsets): Remove a redundant XGetGeometry
call.  If border width is wanted, get it from the XGetGeometry call
instead of calling XGetWindowAttributes on the same window.  Skip some
X calls if we've already detected an error from the X server.
* src/xterm.c (x_wm_supports): Delete x_sync before x_had_errors_p.
(handle_one_xevent): Delete XSync call before x_uncatch_errors.