v0.9.28 - Leftshift of negative value

[TedLyngmo]

asn_INTEGER2long() sets a long to -1 and leftshifts:

        long l;

        // ...

	if((*b >> 7)) l = -1; else l = 0;

	/* Conversion engine */
	for(; b < end; b++)
		l = (l << 8) | *b;

This means we can't turn on UBsan in our gate. This makes UBsan happy:

https://github.com/TedLyngmo/asn1c/tree/v0.9.28-maint-1