Correct an inequality sign causing the bounds check in Windows

Correct an inequality sign causing the bounds check in Windows
palette_set() to be bogus. Fortunately, this isn't exploitable through
the terminal emulator, because the palette escape sequence parser
contains its own bounds check before even calling palette_set().

While I'm at it, fix the same goof in the OS X version! That port is
more or less abandoned, but that's no excuse for leaving obviously
wrong code lying around.

[originally from svn r9965]