Fix NullPointerException in ImsPhoneCallTracker

Fixes a NullPointerException in ImsPhoneCallTracker.getVtDataUsage(). We
must first check that the VideoProvider returned is non-null.

Bug: 29998389
Change-Id: Ia3132a2e8c8f2c5d70528f89cd9af78c857382e5
diff --git a/src/java/com/android/internal/telephony/imsphone/ImsPhoneCallTracker.java b/src/java/com/android/internal/telephony/imsphone/ImsPhoneCallTracker.java
index 79fb74f..663abe3 100644
--- a/src/java/com/android/internal/telephony/imsphone/ImsPhoneCallTracker.java
+++ b/src/java/com/android/internal/telephony/imsphone/ImsPhoneCallTracker.java
@@ -2345,7 +2345,10 @@
         // eventually counted when next getVtDataUsage is called.
         if (mState != PhoneConstants.State.IDLE) {
             for (ImsPhoneConnection conn : mConnections) {
-                conn.getVideoProvider().onRequestConnectionDataUsage();
+                android.telecom.Connection.VideoProvider videoProvider = conn.getVideoProvider();
+                if (videoProvider != null) {
+                    videoProvider.onRequestConnectionDataUsage();
+                }
             }
         }