Telephony: Upgrade: Also migrate empty strings

* If a string is currently empty but not null, it's not copied over when
  upgrading the db, e.g. in copySimInfoValuesV24()
* Change the isEmpty() check to simply check for not null

Change-Id: I8fc98572dd9b6d32c061e87d728ce49d4e063c8c
diff --git a/src/com/android/providers/telephony/TelephonyProvider.java b/src/com/android/providers/telephony/TelephonyProvider.java
index dd43c8a..3e1ffcf 100644
--- a/src/com/android/providers/telephony/TelephonyProvider.java
+++ b/src/com/android/providers/telephony/TelephonyProvider.java
@@ -1998,7 +1998,7 @@
             int columnIndex = c.getColumnIndex(key);
             if (columnIndex != -1) {
                 String fromCursor = c.getString(columnIndex);
-                if (!TextUtils.isEmpty(fromCursor)) {
+                if (fromCursor != null) {
                     cv.put(key, fromCursor);
                 }
             }