Avoid some useless code and memory allocation in case no macro is present

apache2/re_actions.c

@@ -273,6 +273,7 @@ int expand_macros(modsec_rec *msr, msc_string *var, msre_rule *rule, apr_pool_t
                 next_text_start = p + 1;
             }
         } else {
+            if (arr->nelts == 0) return 0; /* no macro */
             /* Text part. */
             part = (msc_string *)apr_pcalloc(mptmp, sizeof(msc_string));
             part->value = apr_pstrdup(mptmp, text_start);