walkDir ignores errors reported by C

[wizzardx]

os.walkDir swallows errors returned from C.

eg, if dir doesn't exist, or device has errors, or permissions are bad, the os.walkDir function always returns successfully.

Example

for p in walkDir("/tmpXXXXX"):
    echo p
echo "Hello"

walkDir will never raise an exception.

This affects Nim 0.19.2.

Related Nim forum discussion thread:

https://forum.nim-lang.org/t/4546