Merge next-mr -> next-4284.

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)

mysql-test/include/check_key_reads.inc

@@ -0,0 +1,6 @@
+# include file for checking if variable key_reads is zero
+let $key_reads= query_get_value(SHOW STATUS LIKE 'key_reads',Value,1);
+--disable_query_log
+eval SELECT IF($key_reads = 0, "Yes!", "No!") as 'Zero key reads?';
+FLUSH STATUS;
+--enable_query_log

mysql-test/include/check_key_req.inc

@@ -0,0 +1,9 @@
+# include file for checking if variable key_reads = key_read_requests
+let $key_reads= query_get_value(SHOW STATUS LIKE 'key_reads',Value,1);
+let $key_r_req= query_get_value(SHOW STATUS LIKE 'key_read_requests',Value,1);
+let $key_writes= query_get_value(SHOW STATUS LIKE 'key_writes',Value,1);
+let $key_w_req= query_get_value(SHOW STATUS LIKE 'key_write_requests',Value,1);
+--disable_query_log
+eval SELECT IF($key_reads = $key_r_req, "reads == requests", "reads != requests") as 'reads vs requests';
+eval SELECT IF($key_writes = $key_w_req, "writes == requests", "writes != requests") as 'writes vs requests';
+--enable_query_log

mysql-test/include/handler.inc

@@ -1491,3 +1491,12 @@ disconnect con1;
 --source include/wait_until_disconnected.inc
 --echo # -> connection default
 connection default;
+
+--echo #
+--echo # A test for Bug#50555 "handler commands crash server in
+--echo # my_hash_first()". 
+--echo #
+--error ER_UNKNOWN_TABLE
+handler no_such_table read no_such_index first;
+--error ER_UNKNOWN_TABLE
+handler no_such_table close;