AVRCP_Browse: Don't send CA attr rsp for empty hdl

Some Remotes go BAD by seeing empty response in the
cover-art handle. Hence, disallow sending cover-art
info if cover-art image handle is empty.

Change-Id: I0ca60c66bf2217af0449ed7f6fd2a54cfc243e39
diff --git a/packages_apps_bluetooth_ext/src/avrcp/Avrcp_ext.java b/packages_apps_bluetooth_ext/src/avrcp/Avrcp_ext.java
index 1c4d06f..94c7f45 100644
--- a/packages_apps_bluetooth_ext/src/avrcp/Avrcp_ext.java
+++ b/packages_apps_bluetooth_ext/src/avrcp/Avrcp_ext.java
@@ -5936,9 +5936,12 @@
     }
 
     public static String getImgHandleFromTitle(byte[] bdaddr, String title) {
+        String handle = null;
         if (DEBUG) Log.d(TAG, " getImgHandleFromTitle bdaddr:" + bdaddr + " title:" + title);
-        if (mAvrcpBipRsp != null && title != null)
-            return mAvrcpBipRsp.getImgHandleFromTitle(bdaddr, title);
-        return "";
+        if (mAvrcpBipRsp != null && title != null) {
+            handle = mAvrcpBipRsp.getImgHandleFromTitle(bdaddr, title);
+            return (handle != null && !handle.isEmpty()) ? handle:null;
+        }
+        return handle;
     }
 }