Fix a few warnings raised by cppcheck

$ cppcheck aha.c  --enable=all
Checking aha.c...
[aha.c:619]: (style) Consecutive return, break, continue, goto or throw statements are unnecessary
[aha.c:77]: (style) Checking if unsigned variable 'digitcount' is less than zero.
Checking usage of global functions..
[aha.c:42]: (style) The function 'getFutureChar' is never used