Fix back button on crypto screen

Did not reenable after entering wrong password.

Bug: 12434219
Change-Id: If8b0c22213a345b3dd0f92e02710c155c7adcd1c

src/com/android/settings/CryptKeeper.java

@@ -209,6 +209,7 @@ public class CryptKeeper extends Activity implements TextView.OnEditorActionList
                         final InputMethodManager imm = (InputMethodManager) getSystemService(
                                                   Context.INPUT_METHOD_SERVICE);
                         imm.showSoftInput(mPasswordEntry, 0);
+                        setBackFunctionality(true);
                     }
                     if (mLockPatternView != null) {
                         mLockPatternView.setEnabled(true);