glib-2.0: Fix potential null pointer dereference in string.joinv()
glib-2.0: Fix potential null pointer dereference in string.joinv()

The logic in the ‘is the array null or empty’ check was disjunctive
rather than conjunctive. If (str_array == null), the condition would
have short-circuited and tried to evaluate str_array.length, which would
have crashed.

Coverity CID: #1462389 (spotted when scanning Tracker)

https://bugzilla.gnome.org/show_bug.cgi?id=791257

frida/vala,frida/vala,GNOME/vala,frida/vala,GNOME/vala,GNOME/vala,frida/vala,GNOME/vala,frida/vala