libc: check name in getvent()/putenv()

passing "", "." or ".." as name caused a crash in
getenv() as it would open the directory; then seek()
to determine the file size would fail and return -1.

now checking for these special names and set
error string when its bad.

doing a single read() will not work when /env has a
9p fileserver mounted onto it and the file size is bigger
than the i/o unit. so doing incremental reads until
we get eof.

0 files changed, 0 insertions, 0 deletions