Fix gigimport in RSA

[JayFoxRox]

Backport of changes that were done in https://github.com/Cxbx-Reloaded/Cxbx-Reloaded/pull/1561

Additionally, an assert was removed because it warns about (what appears to be) a valid state. See this discussion on this PR: #11 (comment)

Hopefully closes #9 and hopefully closes #10

[JayFoxRox]

This assert gets triggered for nxdk XBEs now, because buff is len bytes of zero.

I'm not sure why this check exists in the first place?

[JayFoxRox]

This seems to be a hack that was introduced here: dd70311#diff-e64a6c66ddd61d0fa1f0670ca3423da2L227

---

I don't think the additional check / fixup for g->sign == 0 isn't even necessary, because

xbedump/giants.c

Lines 359 to 377 in d0d6508

	int isZero(
	giant thegiant
	)
	/* Returns TR if thegiant == 0. */
	{
	register int count;
	int length = abs(thegiant->sign);
	register unsigned short * numpointer = thegiant->n;
	if (length)
	{
	for(count = 0; count<length; ++count,++numpointer)
	{
	if (*numpointer != 0 )
	return(FA);
	}
	}
	return(TR);
	}

also checks if the length is zero. So g->sign == 0 appears to be a valid state.

It also handles 0 like that in this:

xbedump/giants.c

Lines 393 to 407 in d0d6508

	void
	itog(
	int i,
	giant g
	)
	/* The giant g becomes set to the integer value i. */
	{
	unsigned int j = abs(i);
	if (i==0)
	{
	g->sign = 0;
	g->n[0] = 0;
	return;
	}

[JayFoxRox]

I've removed this assert.

[chrisderwahre]

I tested this PR on the following:

• 2 Retail Games [XDK Binaries]
• 2 NXDK Binaries

All worked just fine after this change.
Before these changes, NXDK binaries would seg fault. [As this PR also says that it fixes #10 ]

[GXTX]

Tested using the hello sample from nxdk and can confirm it does work as expected. Hopefully we can get another maintainer to verify and merge, thanks.