Missing CatService shall not be treated as exception

CatService is disposed when the relevant SIM is removed or disabled.
StkAppService can also be stopped when the absent state is notified.
RuntimeException shall not be thrown when activity attempts to send a
response to CatService in that situation.

Bug: 131128227
Test: Confirmed that RuntimeException is not thrown after applying this.

Change-Id: I78da77e6aa6c00f09f4dc27f1afb667a58e451c7
diff --git a/src/com/android/stk/StkAppService.java b/src/com/android/stk/StkAppService.java
index cb9564e..e4bfbb6 100644
--- a/src/com/android/stk/StkAppService.java
+++ b/src/com/android/stk/StkAppService.java
@@ -1226,10 +1226,11 @@
         if (mStkService[slotId] == null) {
             mStkService[slotId] = CatService.getInstance(slotId);
             if (mStkService[slotId] == null) {
-                // This should never happen (we should be responding only to a message
-                // that arrived from StkService). It has to exist by this time
-                CatLog.d(LOG_TAG, "Exception! mStkService is null when we need to send response.");
-                throw new RuntimeException("mStkService is null when we need to send response");
+                // CatService is disposed when the relevant SIM is removed or disabled.
+                // StkAppService can also be stopped when the absent state is notified,
+                // so this situation can happen.
+                CatLog.d(LOG_TAG, "No response is sent back to the missing CatService.");
+                return;
             }
         }