Fix a bug in SIGCHLD handler causing 100% CPU usage

The condition breaking the loop were wrong and if there were more child
processes running, the callback fall into unconditional and unwanted
active waiting loop until all these processes exited.

This commit adds an additional condition which breaks the loop if there
is no terminated child.

Closes rhbz#1014085

Signed-off-by: Jakub Filak <jfilak@redhat.com>
Merge pull request #35 from abrt/rhbz1014085

Stop waiting for all children in the signal handler