Handle integer over/under-flow in ast_parse_args

The strtol family of functions will return *_MIN/*_MAX on overflow. To
detect when an overflow has happened, errno must be set to 0 before
calling the function, then checked afterward.

(closes issue ASTERISK-20120)
Reported by: Matt Jordan
Review: https://reviewboard.asterisk.org/r/2073/
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Merged revisions 371392 from http://svn.asterisk.org/svn/asterisk/branches/1.8
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Merged revisions 371398 from http://svn.asterisk.org/svn/asterisk/branches/10
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Merged revisions 371399 from http://svn.asterisk.org/svn/asterisk/branches/11


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