Fix Bug#50555 "handler commands crash server in my_hash_first()"
as a post-merge fix (the new handler tests are not passing 
otherwise).
- in hash.c, don't call calc_hash if ! my_hash_inited().
- add tests and results for the test case for Bug#50555


mysys/hash.c:
  Assert that the hash is initialized when it's used.
sql/set_var.cc:
  Check that the hash is initalized before using it (Bug#50555)