PATCH: Fix crash in pcre_callout with numerical callout 0

We don't use numerical callouts at all, but not crashing is at least a more useful behavior. While it is true that callout_number is always 0 for string callouts, it is not true that it is never 0 for numerical callouts, so check that we got a string too.
---

 Src/Modules/pcre.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Src/Modules/pcre.c b/Src/Modules/pcre.c
index 67157cc016..98b52f8de9 100644
--- a/Src/Modules/pcre.c
+++ b/Src/Modules/pcre.c
@@ -134,7 +134,7 @@ pcre_callout(pcre2_callout_block_8 *block, UNUSED(void *callout_data))
     Eprog prog;
     int ret=0;
 
-    if (!block->callout_number &&
+    if (!block->callout_number && block->callout_string &&
 	    ((prog = parse_string((char *) block->callout_string, 0))))
     {
 	int ef = errflag, lv = lastval;
-- 
2.38.1