1. added check to fill_schema_schemata() func.
   if we have db lookup value we should check that db exists
2. added check to get_all_tables() func
   if we have lookup db name or tables name values we shoud check that
   these values are not empty strings
3. fixed typo


mysql-test/r/information_schema.result:
  test result
mysql-test/t/information_schema.test:
  test case