unbind when leaving activity

This solves the issue where OpenKeyChain shows a dialog even if the application is hidden

app/src/main/java/com/zeapo/pwdstore/crypto/PgpHandler.java

@@ -115,6 +115,12 @@ public class PgpHandler extends Activity implements OpenPgpServiceConnection.OnB
         }
     }
 
+    @Override
+    public void onStop(){
+        super.onStop();
+        this.mServiceConnection.unbindFromService();
+    }
+
     @Override
     public boolean onCreateOptionsMenu(Menu menu) {
         // Inflate the menu; this adds items to the action bar if it is present.
@@ -509,4 +515,9 @@ public class PgpHandler extends Activity implements OpenPgpServiceConnection.OnB
         }
     }
 
+    @Override
+    public void onError(Exception e) {
+
+    }
+
 }