emacsclient: fix child exit when exec fails

* lib-src/emacsclient.c (start_daemon_and_retry_set_socket):
If the execvp of Emacs fails exit instead of having the child
run on and do the work of the parent.  Coalesce duplicate code.
1 job for master in 21 minutes and 19 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Test
failed #129
test

00:21:19

 
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