Bluetooth settings: handle missing permissions

fixes #1637

src/main/java/de/dennisguse/opentracks/settings/SensorsSettingsFragment.java

@@ -2,14 +2,17 @@ package de.dennisguse.opentracks.settings;
 
 import android.os.Bundle;
 import android.util.Log;
+import android.widget.Toast;
 
 import androidx.fragment.app.DialogFragment;
+import androidx.fragment.app.FragmentActivity;
 import androidx.preference.EditTextPreference;
 import androidx.preference.Preference;
 import androidx.preference.PreferenceFragmentCompat;
 
 import de.dennisguse.opentracks.R;
 import de.dennisguse.opentracks.settings.bluetooth.BluetoothLeSensorPreference;
+import de.dennisguse.opentracks.util.PermissionRequester;
 
 public class SensorsSettingsFragment extends PreferenceFragmentCompat {
 
@@ -30,6 +33,13 @@ public class SensorsSettingsFragment extends PreferenceFragmentCompat {
     @Override
     public void onDisplayPreferenceDialog(Preference preference) {
         if (preference instanceof BluetoothLeSensorPreference) {
+            if(!PermissionRequester.BLUETOOTH.hasPermission(preference.getContext())) {
+                // TODO: maybe use requestPermissionsIfNeeded here or disable preferences at all
+                FragmentActivity activity = getActivity();
+                Toast.makeText(activity, getString(R.string.permission_bluetooth_failed), Toast.LENGTH_LONG).show();
+                return;
+            }
+
             DialogFragment dialogFragment = ((BluetoothLeSensorPreference) preference).createInstance();
             dialogFragment.setTargetFragment(this, 0);
             dialogFragment.show(getParentFragmentManager(), getClass().getSimpleName());