Error when reusing WebRequest object

[dchovanec]

When I'm trying to re-use the same WebRequest for multiple subsequent API calls. It fails with error.

I discovered that the Sub Prepare() duplicates headers every time Client.Execute() is called.
I fixed it by modifying the Prepare() with code to update the header [key,value] in case the key is already present.

[timhall]

Ah, that's a good catch! I'll update the code shortly.

[timhall]

@dchovanec Thanks for raising this issue, it's been fixed in v4.0.0-rc.4