Do not compare uninitialized data

Valgrind only seems to complain about memcmp() operations that
actually end up reading uninitialized data, while MemorySanitizer
requires that the entire length of both buffers be defined.

client/mysqltest.cc

@@ -10867,7 +10867,7 @@ REPLACE *init_replace(char * *from, char * *to,uint count,
     for (i=1 ; i <= found_sets ; i++)
     {
       pos=from[found_set[i-1].table_offset];
-      rep_str[i].found= !memcmp(pos, "\\^", 3) ? 2 : 1;
+      rep_str[i].found= !strncmp(pos, "\\^", 3) ? 2 : 1;
       rep_str[i].replace_string=to_array[found_set[i-1].table_offset];
       rep_str[i].to_offset=found_set[i-1].found_offset-start_at_word(pos);
       rep_str[i].from_offset=found_set[i-1].found_offset-replace_len(pos)+

sql/wsrep_xid.cc

@@ -59,6 +59,7 @@ int wsrep_is_wsrep_xid(const void* xid_ptr)
   const XID* xid= static_cast<const XID*>(xid_ptr);
   return (xid->formatID      == 1                   &&
           xid->bqual_length  == 0                   &&
+          xid->gtrid_length  >= static_cast<long>(WSREP_XID_GTRID_LEN_V_1_2) &&
           !memcmp(xid->data, WSREP_XID_PREFIX, WSREP_XID_PREFIX_LEN)      &&
           (((xid->data[WSREP_XID_VERSION_OFFSET] == WSREP_XID_VERSION_1   ||
              xid->data[WSREP_XID_VERSION_OFFSET] == WSREP_XID_VERSION_2)  &&