The problem is introduced by WL#4435 "Support OUT-parameters in 
prepared statements".
When a statement that has out parameters was reprepared,
the reprepare request error was ignored, and an
attempt to send out parameters to the client was made.

Since the out parameter list was not initialized in case
of an error, this attempt led to a crash.

Don't try to send out parameters to the client
if an error occurred in statement execution.

sql/sql_prepare.cc:
  Don't try to send out parameters if error.
tests/mysql_client_test.c:
  Re-enable the test case for Bug#49972.