local: fix sizes and syncing with --links option on Windows - fixes #4581

Before this change rclone returned the size from the Stat call of the
link. On Windows this reads as 0 always, however on unix it reads as
the length of the text in the link. This caused errors like this when
syncing:

    Failed to copy: corrupted on transfer: sizes differ 0 vs 13

This change causes Windows platforms to read the link and use that as
the size of the link instead of 0 which fixes the problem.

backend/local/local.go

@@ -1231,6 +1231,15 @@ func (o *Object) setMetadata(info os.FileInfo) {
 	o.modTime = info.ModTime()
 	o.mode = info.Mode()
 	o.fs.objectMetaMu.Unlock()
+	// On Windows links read as 0 size so set the correct size here
+	if runtime.GOOS == "windows" && o.translatedLink {
+		linkdst, err := os.Readlink(o.path)
+		if err != nil {
+			fs.Errorf(o, "Failed to read link size: %v", err)
+		} else {
+			o.size = int64(len(linkdst))
+		}
+	}
 }
 
 // Stat an Object into info