Handle the case of Alpha Identifier being null.

When Alpha string is NULL, blank screen should not be displayed
for SEND SHORT MESSAGE proactive command.

GCF Testcase UMTS SIM/USIM 27.22.4.10.1 SEND SHORT MESSAGE - SEQ 1.7
diff --git a/src/com/android/stk/StkAppService.java b/src/com/android/stk/StkAppService.java
index aca0c80..f334f74 100644
--- a/src/com/android/stk/StkAppService.java
+++ b/src/com/android/stk/StkAppService.java
@@ -605,7 +605,7 @@
 
     private void launchEventMessage() {
         TextMessage msg = mCurrentCmd.geTextMessage();
-        if (msg == null) {
+        if (msg == null || msg.text == null) {
             return;
         }
         Toast toast = new Toast(mContext.getApplicationContext());