[clang-warning-fix][autological-compare]

Fix following OSX 10.9 clang warning:
/Users/thomas/Devel/oce/src/Draw/Draw.cxx:410:35: warning: comparison of constant 4294967294 with expression of type 'Standard_Boolean' (aka 'bool') is always true [-Wtautological-constant-out-of-range-compare]
    } while (Draw_Interprete(cmd) != (unsigned int ) -2);
             ~~~~~~~~~~~~~~~~~~~~ ^  ~~~~~~~~~~~~~~~~~~
1 warning generated.