Prevent NPE in safety number change dialog.

app/src/main/java/org/thoughtcrime/securesms/conversation/ui/error/SafetyNumberChangeDialog.java

@@ -7,6 +7,7 @@ import android.os.Bundle;
 import android.view.LayoutInflater;
 import android.view.View;
 import android.view.ViewGroup;
+import android.widget.Button;
 
 import androidx.annotation.NonNull;
 import androidx.annotation.Nullable;
@@ -156,13 +157,19 @@ public final class SafetyNumberChangeDialog extends DialogFragment implements Sa
 
     builder.setTitle(R.string.safety_number_change_dialog__safety_number_changes)
            .setView(dialogView)
-           .setCancelable(false)
            .setPositiveButton(continueText, this::handleSendAnyway)
            .setNegativeButton(cancelText, this::handleCancel);
 
     setCancelable(false);
 
-    return builder.create();
+    AlertDialog dialog = builder.create();
+    dialog.setOnShowListener(d -> {
+      Button positive = dialog.getButton(DialogInterface.BUTTON_POSITIVE);
+      positive.setEnabled(false);
+      viewModel.getTrustOrVerifyReady().observe(getViewLifecycleOwner(), positive::setEnabled);
+    });
+
+    return dialog;
   }
 
   @Override

app/src/main/java/org/thoughtcrime/securesms/conversation/ui/error/SafetyNumberChangeViewModel.java

@@ -22,6 +22,8 @@ public final class SafetyNumberChangeViewModel extends ViewModel {
   private final SafetyNumberChangeRepository             safetyNumberChangeRepository;
   private final MutableLiveData<Collection<RecipientId>> recipientIds;
   private final LiveData<SafetyNumberChangeState>        safetyNumberChangeState;
+  private final LiveData<List<ChangedRecipient>>         changedRecipients;
+  private final LiveData<Boolean>                        trustOrVerifyReady;
 
   private SafetyNumberChangeViewModel(@NonNull List<RecipientId> recipientIds,
                                       @Nullable Long messageId,
@@ -31,10 +33,16 @@ public final class SafetyNumberChangeViewModel extends ViewModel {
     this.safetyNumberChangeRepository = safetyNumberChangeRepository;
     this.recipientIds                 = new MutableLiveData<>(recipientIds);
     this.safetyNumberChangeState      = LiveDataUtil.mapAsync(this.recipientIds, ids -> this.safetyNumberChangeRepository.getSafetyNumberChangeState(ids, messageId, messageType));
+    this.changedRecipients            = Transformations.map(safetyNumberChangeState, SafetyNumberChangeState::getChangedRecipients);
+    this.trustOrVerifyReady           = Transformations.map(safetyNumberChangeState, Objects::nonNull);
   }
 
   @NonNull LiveData<List<ChangedRecipient>> getChangedRecipients() {
-    return Transformations.map(safetyNumberChangeState, SafetyNumberChangeState::getChangedRecipients);
+    return changedRecipients;
+  }
+
+  @NonNull LiveData<Boolean> getTrustOrVerifyReady() {
+    return trustOrVerifyReady;
   }
 
   @NonNull LiveData<TrustAndVerifyResult> trustOrVerifyChangedRecipients() {