Hang on UTF-16 with BOM

[chrchr-github]

simplecpp hangs on a file containing a BOM, e.g. \xFF\xFE\x00\x3B.
It looks like there are no tests actually using the FileStream class, or I haven't found them.

[firewave]

It looks like there are no tests actually using the FileStream class, or I haven't found them.

See lengthy discussion in #261. And see #625 for actually implementing it (still mostly a placeholder - too much distractions).