EventManager: check file size for more events

Also add some defensive code

Signed-off-by: Nicola Murino <nicola.murino@gmail.com>

internal/vfs/fileinfo.go

@@ -105,6 +105,9 @@ func (fi *FileInfo) setMetadataFromPointerVal(value map[string]*string) {
 }
 
 func getMetadata(fi os.FileInfo) map[string]string {
+	if fi.Sys() == nil {
+		return nil
+	}
 	if val, ok := fi.Sys().(map[string]string); ok {
 		if len(val) > 0 {
 			return val