Fix for matlab wrapper in sfm.i

[akshay-krishnan]

Changes from pair<size_t, size_t> to IndexPair

[akshay-krishnan]

@varunagrawal would this fix the matlab wrapper? I don't have matlab myself, so wont be able to test it.

[johnwlambert]

Thanks Akshay. Looks fine to me, but I'll defer to the CI and to anyone with a MATLAB license...

I don't understand why this change is necessary, though : - ) IndexPair should compile to a pair of size_t's, looking at its definition:

class IndexPair : public std::pair<size_t,size_t> {

[varunagrawal]

@akshay-krishnan compiles great.

@johnwlambert this seems to be something going on at the compiler level and my guess is it has to do with template matching at compile time. You're specifying the template as IndexPair but using std::pair<size_t, size_t> so perhaps the match is incorrect?

[varunagrawal]

LGTM. I've also added an assertion which was missing.

[akshay-krishnan]

Thanks! We can merge once CI completes.