gmp: fix multiplier with leading zero

[frederikbosch]

Fixes #286

[sagikazarmark]

So is it actually something which can be fixed? Not a limitation of GMP, like in the referenced issue?

[frederikbosch]

@sagikazarmark In the case of issue #278, there was an example that could never be the case inside Money. Why would you want to compare non-integers? That is simply impossible with Money because Money requires the amount to be integer. We never compare non-integers.

But issue #286 is different. One should be able to multiply an amount with decimal leading zero value. As you can see in the multiply method I created a workaround the limitation of GMP.

My point with the calculators is: they are Money internals. Anything inside the calculators that causes bugs inside Money should be fixed. Every other case should be ignored.

[frederikbosch]

@sagikazarmark Decimals within Money are only relevant when multiplying or with divisions. That is why I only created the workaround inside the GMP calculator for multiply and divide. Decimals are irrelevant when adding, subtracting and comparing because Money will always require integers for those methods.

[sagikazarmark]

@frederikbosch okay, agreed.