nih_watch_reader() doesn't handle inotify queue overflow

[James Hunt]

In situations where the kernel is generating events faster than can be consumed by simply ignoring them, nih_watch_handle_by_wd() will cause an assertion failure due to the wd parameter being -1.

This bug is caused by nih_watch_reader() failing to take account of inotify queue overflow, (ironically) resulting in the kernel flooding the application with IN_Q_OVERFLOW events, which crucially specify a watch descriptor of -1.