instructions)

This bug can not be reproduced in the current version,
adding the test case to the test suite for coverage, no code change.


mysql-test/r/sp-code.result:
  Bug#20906 (Multiple assignments in SET in stored routine produce incorrect
  instructions)
mysql-test/t/sp-code.test:
  Bug#20906 (Multiple assignments in SET in stored routine produce incorrect
  instructions)