Auto merge of #116606 - ChrisDenton:empty, r=dtolnay

On Windows make `read_dir` error on the empty path

This makes Windows consistent with other platforms. Note that this should not be taken to imply any decision on #114149 has been taken. However it was felt that while there is a lack of libs-api consensus, we should be consistent across platforms in the meantime.

This is a change in behaviour for Windows so will also need an fcp before merging.

r? libs-api

Author: bors