Fix GCC 4.0.3 warning - size_t cannot be negative
Fix GCC 4.0.3 warning - size_t cannot be negative

ServerMenu.cxx:181: warning: converting negative value ‘-0x00000000000000001’ to ‘size_t’

kongr45gpen/bzflag-import-1,kongr45gpen/bzflag-import-1,kongr45gpen/bzflag-import-1,kongr45gpen/bzflag-import-1,kongr45gpen/bzflag-import-1,kongr45gpen/bzflag-import-1