Errors on sam files with headers

[julistanley]

https://github.com/gwlilabmit/rendseq/blob/3bf0d20e5544ee8f26c2643cc0bc5647a0b3de22/rendseq/make_wig.py#L74C12-L74C36

I had to remove my sam file header to get this line to work. It should ignore a standard SAM header.