mpm_winnt: Remove an unnecessary retry after receiving a non-timeout failure

mpm_winnt: Remove an unnecessary retry after receiving a non-timeout failure
from the mpm_get_completion_context() function.

Currently, the only possible reasons why mpm_get_completion_context() could
fail are real errors such as being unable to WaitForSingleObject(), allocate
memory or create an event.  Retrying under such circumstances doesn't make
sense, and could be as well considered harmful.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1801146 13f79535-47bb-0310-9956-ffa450edef68