Fix bad dimensions of initial frame on VcXsrv

* src/xterm.c (handle_one_xevent) [USE_GTK]: Don't obey
ConfigureNotify events if the frame is not visible.  (Bug#44002)

Copyright-paperwork-exempt: yes
1 job for master in 75 minutes and 55 seconds (queued for 5 seconds)
Status Job ID Name Coverage
  Test
passed #8324
test-all

01:15:55