Simplify gdk_monitor_get_model string duplication

* src/xfns.c (x-display-monitor-attributes-list): Use dupstring over
explicit if/xstrdup.

* src/frame.c (free_monitors): Remove redundant check for NULL.
1 job for master in 49 minutes and 39 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Test
failed #1351
test-all

00:49:39

 
Name Stage Failure
failed
test-all Test
Makefile:313: recipe for target 'check-doit' failed
make[2]: *** [check-doit] Error 1
make[2]: Leaving directory '/builds/emacs/emacs/test'
Makefile:288: recipe for target 'check-expensive' failed
make[1]: *** [check-expensive] Error 2
make[1]: Leaving directory '/builds/emacs/emacs/test'
Makefile:962: recipe for target 'check-expensive' failed
make: *** [check-expensive] Error 2
ERROR: Job failed: exit code 1