Fix Clear Credentials item

This should be enabled whenever there is a credential in the keystore
since there can be unencrypted credentials in there now.

Bug: 8651830
Change-Id: I52a8262011d744d782b35d97deaabcba3b23f32b

src/com/android/settings/SecuritySettings.java

@@ -452,7 +452,7 @@ public class SecuritySettings extends SettingsPreferenceFragment
         }
 
         if (mResetCredentials != null) {
-            mResetCredentials.setEnabled(!mKeyStore.isUnlocked());
+            mResetCredentials.setEnabled(!mKeyStore.isEmpty());
         }
     }