Fix GH-17225: NULL deref in spl_directory.c

NULL checks for the glob stream are inconsistently applied. To solve
this generally, factor it out to a helper function so it's less likely

Fix GH-17225: NULL deref in spl_directory.c

NULL checks for the glob stream are inconsistently applied. To solve
this generally, factor it out to a helper function so it's less likely
to be forgotten in the future.

Closes GH-17231.

show more ...