Fix the issue of new call failing in 3-way call scenario.

The issue this change fixes can be reproduced by:
1. place an MO call;
2. place the second MO call;
3. hangup from the other end for one of the calls so there is only
   one call connected;
4. try to place another call.
This issue is that the new call would fail.

telephony/java/com/android/internal/telephony/cdma/CdmaCallTracker.java

@@ -957,6 +957,7 @@ public final class CdmaCallTracker extends CallTracker {
                 if (ar.exception == null) {
                     // Assume 3 way call is connected
                     pendingMO.onConnectedInOrOut();
+                    pendingMO = null;
                 }
             break;