Fix cursor is empty in ApnEditor

If cursor.moveToFirst() returns false, the cursor is empty which cause
crash.

Check whether the curse is empty to fix.

Fix: 288716180
Test: manual - on ApnEditor page
Test: m RunSettingsRoboTests
Change-Id: If850cd3feca3d3d520a653c2490d1049a8a87fdc

src/com/android/settings/network/apn/ApnEditor.java

@@ -1440,8 +1440,7 @@ public class ApnEditor extends SettingsPreferenceFragment
                 null /* selection */,
                 null /* selectionArgs */,
                 null /* sortOrder */)) {
-            if (cursor != null) {
-                cursor.moveToFirst();
+            if (cursor != null && cursor.moveToFirst()) {
                 apnData = new ApnData(uri, cursor);
             }
         }