Confirm deleting block sender rules

app/src/main/java/eu/faircode/email/FragmentDialogJunk.java

@@ -199,6 +199,12 @@ public class FragmentDialogJunk extends FragmentDialogBase {
         btnClear.setOnClickListener(new View.OnClickListener() {
             @Override
             public void onClick(View v) {
+                new AlertDialog.Builder(v.getContext())
+                        .setTitle(R.string.title_junk_clear)
+                        .setMessage(R.string.title_junk_clear_hint)
+                        .setPositiveButton(android.R.string.ok, new DialogInterface.OnClickListener() {
+                            @Override
+                            public void onClick(DialogInterface dialog, int which) {
                                 Bundle args = new Bundle();
                                 args.putLong("folder", folder);
 
@@ -247,6 +253,15 @@ public class FragmentDialogJunk extends FragmentDialogBase {
                                     }
                                 }.execute(FragmentDialogJunk.this, args, "junk:clear");
                             }
+                        })
+                        .setNegativeButton(android.R.string.cancel, new DialogInterface.OnClickListener() {
+                            @Override
+                            public void onClick(DialogInterface dialog, int which) {
+                                // Do nothing
+                            }
+                        })
+                        .show();
+            }
         });
 
         // Initialize