IAX2: Transfer Reject: Lock bridgecallno before touching it, refactor

1). When touching the bridgecallno, we need to lock it.

2). Remove magic number '0' and replace with TRANSFER_NONE.

3). Exit early if no bridgecallno.

4). Reduce indentation.

Reported by: alecdavis
Tested by: alecdavis
alecdavis (license 585)

Review https://reviewboard.asterisk.org/r/2613/
........

Merged revisions 391333 from http://svn.asterisk.org/svn/asterisk/branches/1.8


git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/11@391334 65c4cc65-6c06-0410-ace0-fbb531ad65f3

channels/chan_iax2.c

@@ -11509,15 +11509,28 @@ immediatedial:
 				}
 				break;
 			case IAX_COMMAND_TXREJ:
-				iaxs[fr->callno]->transferring = 0;
-				ast_verb(3, "Channel '%s' unable to transfer\n", iaxs[fr->callno]->owner ? ast_channel_name(iaxs[fr->callno]->owner) : "<Unknown>");
-				memset(&iaxs[fr->callno]->transfer, 0, sizeof(iaxs[fr->callno]->transfer));
 				if (iaxs[fr->callno]->bridgecallno) {
-					if (iaxs[iaxs[fr->callno]->bridgecallno]->transferring) {
-						iaxs[iaxs[fr->callno]->bridgecallno]->transferring = 0;
-						send_command(iaxs[iaxs[fr->callno]->bridgecallno], AST_FRAME_IAX, IAX_COMMAND_TXREJ, 0, NULL, 0, -1);
+					while (ast_mutex_trylock(&iaxsl[iaxs[fr->callno]->bridgecallno])) {
+						DEADLOCK_AVOIDANCE(&iaxsl[fr->callno]);
+					}
+					if (!iaxs[fr->callno]) {
+						break;
 					}
 				}
+
+				iaxs[fr->callno]->transferring = TRANSFER_NONE;
+				ast_verb(3, "Channel '%s' unable to transfer\n", iaxs[fr->callno]->owner ? ast_channel_name(iaxs[fr->callno]->owner) : "<Unknown>");
+				memset(&iaxs[fr->callno]->transfer, 0, sizeof(iaxs[fr->callno]->transfer));
+
+				if (!iaxs[fr->callno]->bridgecallno) {
+					break;
+				}
+
+				if (iaxs[iaxs[fr->callno]->bridgecallno]->transferring) {
+					iaxs[iaxs[fr->callno]->bridgecallno]->transferring = TRANSFER_NONE;
+					send_command(iaxs[iaxs[fr->callno]->bridgecallno], AST_FRAME_IAX, IAX_COMMAND_TXREJ, 0, NULL, 0, -1);
+				}
+				ast_mutex_unlock(&iaxsl[iaxs[fr->callno]->bridgecallno]);
 				break;
 			case IAX_COMMAND_TXREADY:
 				if (iaxs[fr->callno]->bridgecallno) {