Fix phpGH-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 phpGH-17231.

Author: nielsdos

NEWS

@@ -72,6 +72,9 @@ PHP                                                                        NEWS
     on SO_SNDTIMEO/SO_RCVTIMEO for socket_set_option().
     (David Carlier)
 
+- SPL:
+  . Fixed bug GH-17225 (NULL deref in spl_directory.c). (nielsdos)
+
 - Streams:
   . Fixed bug GH-17037 (UAF in user filter when adding existing filter name due
     to incorrect error handling). (nielsdos)