Bluetooth : UI bug fix : Pairing dialog box takes space as character

- In pairing dialog box even if PIN was removed in text box, still the OK button is enabled
- When length is zero , disable the OK button in pairing dialog
- update fix to prevent error while mOkButton is not ceated.

Change-Id: I38ff3029cff2e7c4e87b7f9c93fa262125e91d44
Signed-off-by: jhtop.kim <jhtop.kim@samsung.com>

src/com/android/settings/bluetooth/BluetoothPairingDialog.java

@@ -297,8 +297,8 @@ public final class BluetoothPairingDialog extends AlertActivity implements
     }
 
     public void afterTextChanged(Editable s) {
-        if (s.length() > 0) {
-            mOkButton.setEnabled(true);
+        if (mOkButton != null) {
+            mOkButton.setEnabled(s.length() > 0);
         }
     }