we changing current db temporarily and restore it when sp is created. however thd->db
in this case becomes empty string rather than NULL and so all checks of thd->db == NULL 
will be false. So if after this we'll issue create procedure sp2()... without specifying
db it will succeed and create sp with db=NULL, which causes mysqldto crash on 
show procedure status statement.

This patch fixes the problem.


mysql-test/r/sp-error.result:
  Result for bug #14569.
mysql-test/t/sp-error.test:
  Test for bug #14569.
sql/sql_db.cc:
  Fixes bug #14569. When no db is selected as current and we do create procedure db.sp()...
  we changing current db temporarily and restore it when sp is created. however thd->db
  in this case becomes empty string rather than NULL and so all checks of thd->db == NULL 
  will be false. This patch fixes this issue.
sql/sql_parse.cc:
  Fixes bug #14569. Reverted from initial patch to check thd->db for null values only.