v4.1.3

Fix - ensure directories return an empty Vinyl (contents: null)

On NetBSD 10 evbarm/aarch64 (Node v22.16.0), fs.readFileSync(dir) returns 4096 bytes instead of throwing EISDIR. This caused vinylFileSync(dir) to succeed, thus loadFile(dir) produced a File with non-null contents, and mem-fs-editor#exists(dir) would incorrectly returns true.