Settings: only set phone number if it's not empty

Only set the phone number in Rename mobile network dialog if it's not
empty in order to preserve the ´Not available´ -text.

Test: m, open ´SIMs´ in settings, click Pen-icon to edit SIM, verify
      either mobile number or ´Not available´ -text is shown.
Change-Id: I3bc1f1f4eb26cda38e5cc7a12bd4db1bf922f076

src/com/android/settings/network/telephony/RenameMobileNetworkDialogFragment.java

@@ -184,7 +184,10 @@ public class RenameMobileNetworkDialogFragment extends InstrumentedDialogFragmen
         phoneTitle.setVisibility(info.isOpportunistic() ? View.GONE : View.VISIBLE);
 
         final TextView phoneNumber = view.findViewById(R.id.number_value);
-        phoneNumber.setText(DeviceInfoUtils.getBidiFormattedPhoneNumber(getContext(), info));
+        final String pn = DeviceInfoUtils.getBidiFormattedPhoneNumber(getContext(), info);
+        if (!TextUtils.isEmpty(pn)) {
+            phoneNumber.setText(pn);
+        }
     }
 
     @Override