emacsclient: coalesce WINDOWSNT-specific code

* lib-src/emacsclient.c (sock_err_message) [WINDOWSNT]:
Do nothing if w32_window_app () && alternate_editor.
Both callers changed.
1 job for master in 22 minutes and 9 seconds (queued for 6 seconds)
Status Job ID Name Coverage
  Test
failed #123
test

00:22:09

 
Name Stage Failure
failed
test Test
Makefile:301: recipe for target 'check-doit' failed
make[2]: *** [check-doit] Error 1
make[2]: Leaving directory '/builds/tzz/emacs/test'
Makefile:271: recipe for target 'check' failed
make[1]: *** [check] Error 2
make[1]: Leaving directory '/builds/tzz/emacs/test'
Makefile:955: recipe for target 'check' failed
make: *** [check] Error 2
ERROR: Job failed: exit code 1