Update CI and code to use Staticcheck v0.5.1

This fixes a few code errors that slipped through review (thankfully now
handled by Staticcheck for us) and makes sure we are using the latest
version.

.github/workflows/static_analysis.yml

@@ -33,7 +33,7 @@ jobs:
       run: |
         go install golang.org/x/tools/cmd/goimports@latest
         go install github.com/fzipp/gocyclo/cmd/gocyclo@latest
-        go install honnef.co/go/tools/cmd/staticcheck@v0.4.6
+        go install honnef.co/go/tools/cmd/staticcheck@v0.5.1
         go install github.com/mattn/goveralls@latest
 
     - name: Vet

cmd/fyne/internal/mobile/binres/binres_test.go

@@ -246,7 +246,7 @@ func compareElements(have, want *XML) error {
 		}
 	}
 	if buf.Len() > 0 {
-		return fmt.Errorf(buf.String())
+		return errors.New(buf.String())
 	}
 	return nil
 }

widget/check_group.go

@@ -182,7 +182,7 @@ type checkGroupRenderer struct {
 // Layout the components of the checks widget
 func (r *checkGroupRenderer) Layout(_ fyne.Size) {
 	count := 1
-	if r.items != nil && len(r.items) > 0 {
+	if len(r.items) > 0 {
 		count = len(r.items)
 	}
 	var itemHeight, itemWidth float32

widget/list.go

@@ -169,7 +169,7 @@ func (l *List) scrollTo(id ListItemID) {
 	separatorThickness := l.Theme().Size(theme.SizeNamePadding)
 	y := float32(0)
 	lastItemHeight := l.itemMin.Height
-	if l.itemHeights == nil || len(l.itemHeights) == 0 {
+	if len(l.itemHeights) == 0 {
 		y = (float32(id) * l.itemMin.Height) + (float32(id) * separatorThickness)
 	} else {
 		for i := 0; i < id; i++ {
@@ -368,7 +368,7 @@ func (l *List) contentMinSize() fyne.Size {
 	}
 	items := l.Length()
 
-	if l.itemHeights == nil || len(l.itemHeights) == 0 {
+	if len(l.itemHeights) == 0 {
 		return fyne.NewSize(l.itemMin.Width,
 			(l.itemMin.Height+separatorThickness)*float32(items)-separatorThickness)
 	}

widget/radio_group.go

@@ -156,7 +156,7 @@ type radioGroupRenderer struct {
 // Layout the components of the radio widget
 func (r *radioGroupRenderer) Layout(_ fyne.Size) {
 	count := 1
-	if r.items != nil && len(r.items) > 0 {
+	if len(r.items) > 0 {
 		count = len(r.items)
 	}
 	var itemHeight, itemWidth float32