pbx_spool: Gracefully handle long lines in call files

Per the linked issue, we aren't checking the buffer filled by fgets()
to determine if it contains a newline, so we will fail to correctly
parse the trailing portion of a long line.

This patch increases the buffer size from 256 to 1024, and skips any
line that exceeds that length, logging a warning in the process.

ASTERISK-17067 #close
Reported by: Dave Olszewski

Change-Id: I51bcf270c1b4347ba05b43f18dc2094c76f5d7b0