libmodplug calls `cctype` functions, such as `isspace`,
with negative values. This is undefined behaviour.

While glibc allows it, it crashes on uClibc compiled
without `UCLIBC_HAS_CTYPE_SIGNED`.

Adds a patch that resolves the issue.

Also sent upstream. However, the library author has not merged
any pull request for about a year.

Signed-off-by: Gleb Mazovetskiy <glex.spb@gmail.com>
[yann.morin.1998@free.fr:
  - add Gleb's SoB to the patch
  - add upstream URL to the patch
]
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>