Fix processing of call files when using KQueue on OS X

In certain situations, call files are not processed when using KQueue with
pbx_spool. Asterisk was sending an invalid timeout value when the spool
directory is empty, causing the call to kevent to error immediately. This
can create a tight loop, increasing the CPU load on the system.

(closes issue ASTERISK-21176)
Reported by: Carlton O'Riley
patches:
  kqueue_osx.patch uploaded by coriley (License 6473)
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Merged revisions 383120 from http://svn.asterisk.org/svn/asterisk/branches/1.8
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Merged revisions 383121 from http://svn.asterisk.org/svn/asterisk/branches/11


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@383122 65c4cc65-6c06-0410-ace0-fbb531ad65f3