[Fix] Clear the buffer before reading again, fixes #279

[manthanabc]

Fixes the invalid environment variable issue

There was hash prepended to the actual environment variables string received from swhks
since UnixStream::read_to_string method is append to buffer instead of overwriting, the result of previous read still persists in the buffer resulting in invalid variable.

This happens when the previous hash do not match and hence request for latest variables is made to swhks and read into the same buffer hash was read in (which appends).

Fix

clear the buffer before reading next string.

Fixes #279

[newtoallofthis123]

The buffer clearing should not have been overlooked!
Thanks for the PR!

Anywhere else the #279 bug can creep in that you can find?

[manthanabc]

Anywhere else the #279 bug can creep in that you can find?

I tried to find it, i don't think similar bug exists anywhere else.

[newtoallofthis123]

That's cool
Thanks for the PR :)