Fix mod_include potential segfault checking backref from unmatched regexp

http://markmail.org/message/jlc7t5edsjujbe37
Patch by rpluem, lars, niq


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@795445 13f79535-47bb-0310-9956-ffa450edef68

include/ap_expr.h

@@ -73,6 +73,7 @@ typedef struct {
     const char *rexp;
     apr_size_t  nsub;
     ap_regmatch_t match[AP_MAX_REG_MATCH];
+    int have_match;
 } backref_t;
 
 typedef const char *(*string_func_t)(request_rec*, const char*);