Intel bugfix

I think I found a bug in bcf1_sync() function. The detailed explanation is in the 2 commit messages.
Apologies for the mess with the whitespace: I add the string ?w=1 to github urls to ignore whitespace changes
https://github.com/kgururaj/htslib/commit/5fb89e33e2c2334df1050eb127d71f9a3fc36c8d?w=1