Fix plugin loading in electron

[campersau]

I made a mistake in #1350 which prevented ungit from beeing loaded in electron. I assumend that fs.readdir(..., { withFileTypes: true }) would just work in electron but since we are using asar it apparently does not. See electron/electron#19074

First commit refactors the code to the fs.readdir and fs.stat equivalent.
The second commit gets rid of the directory check completely because we already catch and ignore all errors 😄