fixes ability to exit echo app

when called from a ISDN channel, null frames prevent '#' exit.
Now only echo back VOICE and DTMF frames

(issue #16880)
Reported by: alecdavis
Patches: 
      echo_exit.diff.txt uploaded by alecdavis (license 585)
Tested by: alecdavis



git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@249801 65c4cc65-6c06-0410-ace0-fbb531ad65f3

apps/app_echo.c

@@ -62,17 +62,26 @@ static int echo_exec(struct ast_channel *chan, const char *data)
 		if (!f) {
 			break;
 		}
-		f->delivery.tv_sec = 0;
-		f->delivery.tv_usec = 0;
-		if (ast_write(chan, f)) {
-			ast_frfree(f);
-			goto end;
-		}
-		if ((f->frametype == AST_FRAME_DTMF) && (f->subclass.integer == '#')) {
-			res = 0;
-			ast_frfree(f);
-			goto end;
-		}
+		switch (f->frametype) {
+		case AST_FRAME_VOICE:
+		case AST_FRAME_DTMF:
+			f->delivery.tv_sec = 0;
+			f->delivery.tv_usec = 0;
+			if (ast_write(chan, f)) {
+				ast_frfree(f);
+				goto end;
+			}
+			if (f->frametype == AST_FRAME_DTMF) {
+				if (f->subclass.integer == '#') {
+					res = 0;
+					ast_frfree(f);
+					goto end;
+				}
+			}
+			break;
+		default:
+			break;
+		}		
 		ast_frfree(f);
 	}
 end: