gsn_restart file: wrap umask change tightly around file creation

An fopen("w") error used to omit the umask() call to reinstate the previous
umask. Also an fopen("r") at the top will never create a file and hence does
not need a umask set.

Instead, wrap the umask change and change-back tightly around the single
fopen("w") call.

Change-Id: If7d948e2f2ba47ecebba5614f18235a53b273d14
1 file changed