say.c: Honor requests for DTMF interruption.

SayAlpha, SayAlphaCase, SayDigits, SayMoney, SayNumber, SayOrdinal,
and SayPhonetic all claim to allow DTMF interruption if the
SAY_DTMF_INTERRUPT channel variable is set to a truthy value, but we
are failing to break out of a given 'say' application if DTMF actually
occurs.

ASTERISK-29816 #close

Change-Id: I6a96e0130560831d2cb45164919862b9bcb6287e
(cherry picked from commit 4fe94bab09)

main/say.c

@@ -189,6 +189,13 @@ static int say_filenames(struct ast_channel *chan, const char *ints, const char
 				res = ast_waitstream_full(chan, ints, audiofd, ctrlfd);
 			else
 				res = ast_waitstream(chan, ints);
+
+			if (res > 0) {
+				/* We were interrupted by a digit */
+				ast_stopstream(chan);
+				ast_free(filenames);
+				return res;
+			}
 		}
 		ast_stopstream(chan);
 	}