fs: fix fs.readFile, fs.exists{Sync} regression caused by assertions
Checklist
-
make -j4 test
(UNIX), orvcbuild test
(Windows) passes -
tests and/or benchmarks are included -
documentation is changed or added -
commit message follows commit guidelines
Affected core subsystem(s)
fs
Refs: https://github.com/nodejs/node/pull/17667
https://github.com/nodejs/node/pull/17667 didn't include the path validation of these methods in JS land, so passing undefined as paths to them would go straight to assertions, which caused CITGM regression https://ci.nodejs.org/view/Node.js-citgm/job/citgm-smoker/1165/ . This PR fixes that by adding those validations back.