core: check that regex is not NULL in function string_regcomp

src/core/wee-string.c

@@ -922,6 +922,9 @@ string_regcomp (void *preg, const char *regex, int default_flags)
     const char *ptr_regex;
     int flags;
 
+    if (!regex)
+        return -1;
+
     ptr_regex = string_regex_flags (regex, default_flags, &flags);
     return regcomp ((regex_t *)preg, ptr_regex, flags);
 }