Bug#34991760 query_rewrite_plugins.logging_general_raw test crashes with FORTIFY_SOURCE=3

A digest in the query rewrite plugin is always 32 bytes long.
Fix bad arguments to snprintf.

Change-Id: Ib46855206384fb4c23b3850502ad0c19e612c831
(cherry picked from commit bcf84d9cc1963b255eb04ff1a3741e40ea055f77)

Author: Tor Didriksen

plugin/rewriter/services.cc

@@ -39,10 +39,9 @@ using std::string;
 namespace services {
 
 string print_digest(const unsigned char *digest) {
-  const size_t string_size = PARSER_SERVICE_DIGEST_LENGTH * 2;
-  char digest_str[string_size + sizeof('\0')];
+  char digest_str[2 * PARSER_SERVICE_DIGEST_LENGTH + 1];
   for (int i = 0; i < PARSER_SERVICE_DIGEST_LENGTH; ++i)
-    snprintf(digest_str + i * 2, string_size, "%02x", digest[i]);
+    sprintf(digest_str + i * 2, "%02x", digest[i]);
   return digest_str;
 }