filter: fix deadlock with errors on --files-from

Before this change if doing a recursive directory listing with
`--files-from` if more than `--checkers` files errored (other than
file not found) then rclone would deadlock.

This fixes the problem by exiting on the first error.

fs/filter/filter.go

@@ -433,13 +433,13 @@ func (f *Filter) MakeListR(ctx context.Context, NewObject func(ctx context.Conte
 		var (
 			checkers = ci.Checkers
 			remotes  = make(chan string, checkers)
-			g        errgroup.Group
+			g, gCtx  = errgroup.WithContext(ctx)
 		)
 		for i := 0; i < checkers; i++ {
 			g.Go(func() (err error) {
 				var entries = make(fs.DirEntries, 1)
 				for remote := range remotes {
-					entries[0], err = NewObject(ctx, remote)
+					entries[0], err = NewObject(gCtx, remote)
 					if err == fs.ErrorObjectNotFound {
 						// Skip files that are not found
 					} else if err != nil {
@@ -454,8 +454,13 @@ func (f *Filter) MakeListR(ctx context.Context, NewObject func(ctx context.Conte
 				return nil
 			})
 		}
+	outer:
 		for remote := range f.files {
-			remotes <- remote
+			select {
+			case remotes <- remote:
+			case <-gCtx.Done():
+				break outer
+			}
 		}
 		close(remotes)
 		return g.Wait()

fs/filter/filter_test.go

@@ -360,6 +360,15 @@ func TestNewFilterMakeListR(t *testing.T) {
 	require.NoError(t, f.AddFile("error"))
 	err = listR(context.Background(), "", listRcallback)
 	require.EqualError(t, err, assert.AnError.Error())
+
+	// The checker will exit by the error above
+	ci := fs.GetConfig(context.Background())
+	ci.Checkers = 1
+
+	// Now check an error is returned from NewObject
+	require.NoError(t, f.AddFile("error"))
+	err = listR(context.Background(), "", listRcallback)
+	require.EqualError(t, err, assert.AnError.Error())
 }
 
 func TestNewFilterMinSize(t *testing.T) {