The problem is that the query cache was storing partial results
if the statement failed when sending the results to the client.
This could cause clients to hang when trying to read the results
from the cache as they would, for example, wait indefinitely for
a eof packet that wasn't saved.

The solution is to always discard the caching of a query that
failed to send its results to the associated client.

mysql-test/r/query_cache_notembedded.result:
  Add test case result for Bug#40264
mysql-test/t/query_cache_notembedded.test:
  Add test case for Bug#40264
sql/sql_cache.cc:
  Abort if a unreported error was raised.