Minor fix in .gdbinit

* src/.gdbinit (xprintsym): Don't attempt to print the
symbol's name if it is not yet set.  This happens with
built-in symbols at the beginning of 'main'.
1 job for master in 55 minutes and 13 seconds (queued for 1 second)
Status Job ID Name Coverage
  Test
failed #1641
test-all

00:55:13

 
Name Stage Failure
failed
test-all Test
Makefile:315: recipe for target 'check-doit' failed
make[2]: Leaving directory '/builds/emacs/emacs/test'
make[2]: *** [check-doit] Error 1
Makefile:290: recipe for target 'check-expensive' failed
make[1]: *** [check-expensive] Error 2
make[1]: Leaving directory '/builds/emacs/emacs/test'
Makefile:957: recipe for target 'check-expensive' failed
make: *** [check-expensive] Error 2
ERROR: Job failed: exit code 1