--skip-grant-tables. However when deleting functions UDFs list was checked
regardless of whther UDFs are initialized or not. Additional check is added
into free_udf() and find_udf() functions to prevent possible runtime errors.


mysql-test/r/skip_grants.result:
  Test result for #17595 patch.
mysql-test/t/skip_grants.test:
  Test for #17595 patch.