app_dial: Fix progress timeout calculation with no answer timeout.

If to_answer is -1, simply comparing to see if the progress timeout
is smaller than the answer timeout to prefer it will fail. Add
an additional check that chooses the progress timeout if there is
no answer timeout (or as before, if the progress timeout is smaller).

Resolves: #821
(cherry picked from commit 6a07e8e0f1)

apps/app_dial.c

@@ -1292,7 +1292,7 @@ static struct ast_channel *wait_for_answer(struct ast_channel *in,
 		}
 
 		/* If progress timeout is active, use that if it's the shorter of the 2 timeouts. */
-		winner = ast_waitfor_n(watchers, pos, *to_progress > 0 && *to_progress < *to_answer ? to_progress : to_answer);
+		winner = ast_waitfor_n(watchers, pos, *to_progress > 0 && (*to_answer < 0 || *to_progress < *to_answer) ? to_progress : to_answer);
 
 		AST_LIST_TRAVERSE(out_chans, o, node) {
 			int res = 0;