[android] address review comments for rejecting unsupported images

briar-android/src/main/java/org/briarproject/briar/android/attachment/AttachmentCreationTask.java

@@ -106,8 +106,7 @@ class AttachmentCreationTask {
 		return h;
 	}
 
-	private boolean isValidMimeType(@Nullable String mimeType) {
+	private boolean isValidMimeType(String mimeType) {
-		if (mimeType == null) return false;
 		for (String supportedType : IMAGE_MIME_TYPES) {
 			if (supportedType.equals(mimeType)) return true;
 		}

briar-android/src/main/java/org/briarproject/briar/android/attachment/AttachmentCreator.java

@@ -64,21 +64,10 @@ public class AttachmentCreator {
 
 	@UiThread
 	public LiveData<AttachmentResult> storeAttachments(
-			LiveData<GroupId> groupId, Collection<Uri> newUris, boolean restart) {
+			LiveData<GroupId> groupId, Collection<Uri> newUris) {
-		MutableLiveData<AttachmentResult> result;
-		if (restart) {
-			// This can happen due to configuration changes.
-			// So don't create new attachments. They are already being created
-			// and returned by the existing LiveData.
-			result = this.result;
-			if (task == null || uris.isEmpty() || result == null)
-				throw new IllegalStateException();
-			// A task is already running. It will update the result LiveData.
-			// So nothing more to do here.
-		} else {
 		if (this.result != null || !uris.isEmpty())
 			throw new IllegalStateException();
-			result = new MutableLiveData<>();
+		MutableLiveData<AttachmentResult> result = new MutableLiveData<>();
 		this.result = result;
 		uris.addAll(newUris);
 		observeForeverOnce(groupId, id -> {
@@ -88,7 +77,22 @@ public class AttachmentCreator {
 					app.getContentResolver(), this, id, uris, needsSize);
 			ioExecutor.execute(() -> task.storeAttachments());
 		});
+		return result;
 	}
+
+	/**
+	 * This should be only called after configuration changes.
+	 * In this case we should not create new attachments.
+	 * They are already being created and returned by the existing LiveData.
+	 */
+	@UiThread
+	public LiveData<AttachmentResult> getLiveAttachments() {
+		//
+		MutableLiveData<AttachmentResult> result = this.result;
+		if (task == null || uris.isEmpty() || result == null)
+			throw new IllegalStateException();
+		// A task is already running. It will update the result LiveData.
+		// So nothing more to do here.
 		return result;
 	}
 

briar-android/src/main/java/org/briarproject/briar/android/conversation/ConversationViewModel.java

@@ -199,9 +199,12 @@ public class ConversationViewModel extends AndroidViewModel
 	@UiThread
 	public LiveData<AttachmentResult> storeAttachments(Collection<Uri> uris,
 			boolean restart) {
+		if (restart) {
+			return attachmentCreator.getLiveAttachments();
+		} else {
 			// messagingGroupId is loaded with the contact
-		return attachmentCreator
+			return attachmentCreator.storeAttachments(messagingGroupId, uris);
-				.storeAttachments(messagingGroupId, uris, restart);
+		}
 	}
 
 	@Override