description size is added twice

[johnsdouglass]

https://github.com/OzymandiasTheGreat/klembord/blob/44b1d4f756b12a887641a4e1d5961cad287bf3be/klembord/winclipboard.py#L220

Since html_header_size already includes the description size, this line and the two lines after it calculate the sizes incorrectly.

Removing description_size+ from these lines fixes the problem.

[marmidr]

Fix suggestion: https://github.com/OzymandiasTheGreat/klembord/pull/21