orcbytecode: Fix parsing of 64 bit values from bytecode

The shift by 24 bits has to be casted already, otherwise we shift
into the sign bit which causes undefined behaviour.

Thanks to Edward Hervey for debugging this.

https://bugzilla.gnome.org/show_bug.cgi?id=698520
orcbytecode: Fix parsing of 32 bit values from bytecode as well

The shift by 24 bits has to be casted as well, otherwise we
shift into the sign bit which causes undefined behaviour.

See https://bugzilla.gnome.org/show_bug.cgi?id=698520