during EXPLAIN

Before the patch, send_eof() of some subclasses of 
select_result (e.g., select_send::send_eof()) could 
handle being called after an error had occured while others 
could not. The methods that were not well-behaved would trigger
an ASSERT on debug builds. Release builds were not affected.

Consider the following query as an example for how the ASSERT
could be triggered:

A user without execute privilege on f() does
   SELECT MAX(key1) INTO @dummy FROM t1 WHERE f() < 1;
resulting in "ERROR 42000: execute command denied to user..." 

The server would end the query by calling send_eof(). The 
fact that the error had occured would make the ASSERT trigger. 

select_dumpvar::send_eof() was the offending method in the
bug report, but the problem also applied to other 
subclasses of select_result. This patch uniforms send_eof() 
of all subclasses of select_result to handle being called 
after an error has occured. 

mysql-test/r/not_embedded_server.result:
  Added test for BUG#54812
mysql-test/t/not_embedded_server.test:
  Added test for BUG#54812
sql/sql_class.cc:
  send_eof() of all subclasses of select_result can now handle being
  called after an error has occured.
sql/sql_insert.cc:
  send_eof() of all subclasses of select_result can now handle being
  called after an error has occured.
  Also fix call to abort() in select_create::send_eof(), which was supposed to abort the result set, not terminate the server. This call to abort() should have been changed when the function was renamed from abort_result_set() but was forgotten. New test case added by BUG#54812 covered this line and terminated server.
sql/sql_prepare.cc:
  send_eof() of all subclasses of select_result can now handle being
  called after an error has occured.
sql/sql_update.cc:
  send_eof() of all subclasses of select_result can now handle being
  called after an error has occured.