This patch corrects a misstake in the test case for bug patch 43658.

There was a race in the test case when the thread id was retrieved from the processlist.
The result was that the same thread id was signalled twice and one thread id wasn't
signalled at all.

The affected platforms appears to be limited to linux.

mysql-test/r/query_cache_debug.result:
  There was a race in the test case when the thread id was retrieved from the processlist.
  The result was that the same thread id was signalled twice and one thread id wasn't
  signalled at all.
mysql-test/t/query_cache_debug.test:
  There was a race in the test case when the thread id was retrieved from the processlist.
  The result was that the same thread id was signalled twice and one thread id wasn't
  signalled at all.