Fix stack effect

[thautwarm]

Fix https://github.com/vstinner/bytecode/issues/38.
@MatthieuDartiailh
If dis.stack_effect doesn't convert oparg when unnecessarily, we wouldn't get this error.

https://github.com/python/cpython/blob/137b0632dccb992ca11e9445142fb33a29c33a51/Modules/_opcode.c#L38

However, for we cannot change the standard module immediately, we have to avoid passing the oparg when we didn't calculate the operand of an instruction.

For instance, Instr('LOAD_CONST', 0xFFFFFFFFFFFFFFF) might donate bytecode LOAD_CONST 1, and when we calculate its stack effect, we should use dis.stack_effect(100, 1) instead of dis.stack_effect(100, 0xFFFFFFFFFFFFFFF).

Actually we cannot convert 0xFFFFFFFFFFFFFFF to 1 when calculating stack effects, fortunately if we have to convert the oparg of Instr to the operand of bytecode instruction, it means that the oparg is insignificant to the result.

Thanks @serhiy-storchaka for
https://github.com/python/cpython/blob/137b0632dccb992ca11e9445142fb33a29c33a51/Python/compile.c#L859.

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@@            Coverage Diff            @@
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Impacted Files	Coverage Δ
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bytecode/tests/test_instr.py	98.59% <100%> (ø)

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[SnoopyLane]

For instance, Instr('LOAD_CONST', 0xFFFFFFFFFFFFFFF) might donate bytecode LOAD_CONST 1, and when we calculate its stack effect, we should use dis.stack_effect(100, 1) instead of dis.stack_effect(100, 0xFFFFFFFFFFFFFFF).

This is a subtle but critical detail. Thanks for the reminder!

[MatthieuDartiailh]

Some minor comment edits suggestion (this new Github feature is great !) but otherwise this is good to go. Please check the length of the lines of my edits github does not provide yet rulers.