mount: update the file size so file Attr() can read

if file Attr() during file writes, the OS, at least for Mac, may try to resend the data to write, which usually are empty.

weed/filesys/filehandle.go

@@ -102,6 +102,8 @@ func (fh *FileHandle) Write(ctx context.Context, req *fuse.WriteRequest, resp *f
 
 	// write the request to volume servers
 
+	fh.f.entry.Attributes.FileSize = uint64(max(req.Offset+int64(len(req.Data)), int64(fh.f.entry.Attributes.FileSize)))
+
 	chunks, err := fh.dirtyPages.AddPage(ctx, req.Offset, req.Data)
 	if err != nil {
 		glog.Errorf("%+v/%v write fh %d: [%d,%d): %v", fh.f.dir.Path, fh.f.Name, fh.handle, req.Offset, req.Offset+int64(len(req.Data)), err)