girparser: Silence a scan-build NULL pointer dereference warning

It’s very obviously a false positive, as `str` has been added to on the
previous line, so can’t be `(void *) 0`. Not sure what scan-build is
thinking.

I’d rather not have this assertion (it doesn’t help the programmer’s
understanding of the code), but I would also rather have scan-build
running with no warnings so that it can helpfully catch newly-introduced
errors in future.

Signed-off-by: Philip Withnall <pwithnall@gnome.org>

Helps: #1767

girepository/girparser.c

@@ -670,6 +670,9 @@ parse_type_internal (GIIrModule   *module,
       type->is_pointer = TRUE;
       str += strlen ("Error");
 
+      /* Silence a scan-build false positive */
+      g_assert (str != NULL);
+
       if (*str == '<')
         {
           char *tmp, *end;