If, after the tables are locked, one of the conditions to read from a
HANDLER table is not met, the handler code wrongly jumps to a error path
that won't unlock the tables.

The user-visible effect is that after a error in a handler read command,
all subsequent handler operations on the same table will hang.

The fix is simply to correct the code to jump to the (same) error path that
unlocks the tables.


mysql-test/r/handler.result:
  Bug#30632 test case result
mysql-test/t/handler.test:
  Bug#30632 test case
sql/sql_handler.cc:
  Always unlock the internal and external table level locks if any of the conditions
  (including errors) to read from a HANDLER table are not met.