Ignore invalid symlinks for files that would be skipped anyway

Previously, SketchLoad would error out on *any* error during file
enumeration, including broken symlinks (where `os.Stat` returns
`ErrNotExist`), even when that symlink would not be loaded (i.e. no
valid extension) anyway.

Now, `ErrNotExist` errors are ignored and a broken symlink is processed
as normal. This changes the code to assume broken symlinks are not
directories and to use the `path` value instead of the `info.Name()`,
since the latter is not available when the `Stat()` call failed.

If, based on the name of the broken symlink, the file would be skipped,
processing continues as normal. If the file would be loaded, then the
existing `os.Open()` call fails (and since the previous commit, returns
an error like before for all broken symlinks).

Author: matthijskooijman

Diff for: arduino/builder/sketch.go

@@ -154,12 +154,15 @@ func SketchLoad(sketchPath, buildPath string) (*sketch.Sketch, error) {
 	var files []string
 	rootVisited := false
 	err = simpleLocalWalk(sketchFolder, maxFileSystemDepth, func(path string, info os.FileInfo, err error) error {
-		if err != nil {
+		// Ignore ErrNotExist (broken symlinks), which will be
+		// reported by os.Open below if the file would not be
+		// skipped based on the name
+		if err != nil && !errors.Is(err, os.ErrNotExist) {
 			feedback.Errorf("Error during sketch processing: %v", err)
 			os.Exit(errorcodes.ErrGeneric)
 		}
 
-		if info.IsDir() {
+		if info != nil && info.IsDir() {
 			// Filters in this if-block are NOT applied to the sketch folder itself.
 			// Since the sketch folder is the first one processed by simpleLocalWalk,
 			// we can set the `rootVisited` guard to exclude it.
@@ -182,7 +185,7 @@ func SketchLoad(sketchPath, buildPath string) (*sketch.Sketch, error) {
 		}
 
 		// ignore hidden files
-		if strings.HasPrefix(info.Name(), ".") {
+		if strings.HasPrefix(filepath.Base(path), ".") {
 			return nil
 		}