res_agi: Add message indicating need for \n character in verbose message

The while loop responsible for reading AGI messages from a fastAGI service
can end up looping indefinitely when an AGI script fails to indicate the end
of a message with a \n character. This patch adds an indication that we are
expecting a \n character to end the message to make it more clear to users
that this is necessary if they are receiving this warning over and over.

(issue ASTERISK-20061)
Reported by: Eike Kuiper
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Merged revisions 370494 from http://svn.asterisk.org/svn/asterisk/branches/1.8
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Merged revisions 370495 from http://svn.asterisk.org/svn/asterisk/branches/10


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@370510 65c4cc65-6c06-0410-ace0-fbb531ad65f3

res/res_agi.c

@@ -3581,7 +3581,7 @@ static enum agi_result run_agi(struct ast_channel *chan, char *request, AGI *agi
 					break;
 				len = sizeof(buf) - buflen;
 				if (agidebug)
-					ast_verbose( "AGI Rx << temp buffer %s - errno %s\n", buf, strerror(errno));
+					ast_verbose("AGI Rx << temp buffer %s - errno %s\nNo \\n received, checking again.\n", buf, strerror(errno));
 			}
 
 			if (!buf[0]) {