BUG#13555854: CHECK AND REPAIR TABLE SHOULD BE MORE ROBUST [1]

ISSUE: Incorrect key file. Key file is corrupted,
       Reading incorrect key information (keyseg)
       from index file. Key definition in .MYI
       and .FRM file differs. Starting pointer
       to read the keyseg information is changed
       to a value greater than the pack_reclength.
       Memcpy tries to read keyseg information from
       unallocated memory which causes the crash.

SOLUTION: One more check added to compare the
          the key definition in .MYI and .FRM
          file. If the definition differ, server
          produces an error.

storage/myisam/ha_myisam.cc

@@ -516,7 +516,8 @@ int check_definition(MI_KEYDEF *t1_keyinfo, MI_COLUMNDEF *t1_recinfo,
           t1_keysegs[j].language != t2_keysegs[j].language) ||
           t1_keysegs_j__type != t2_keysegs[j].type ||
           t1_keysegs[j].null_bit != t2_keysegs[j].null_bit ||
-          t1_keysegs[j].length != t2_keysegs[j].length)
+          t1_keysegs[j].length != t2_keysegs[j].length ||
+          t1_keysegs[j].start != t2_keysegs[j].start)
       {
         DBUG_PRINT("error", ("Key segment %d (key %d) has different "
                              "definition", j, i));