Error when using `iter_aij` on sparse matrix

[mscroggs]

I'm getting index out of bounds error on csr_mat.rs:182:49

Looks like it's an issue when this runs when obtaining the last entry in the matrix:

rlst/src/sparse/sparse_mat/csr_mat.rs

Lines 181 to 184 in ddafa6c

	// The following jumps over all zero rows to the next relevant row
	while self.row < self.mat.shape()[0] && self.mat.indptr()[1 + self.row] <= self.pos {
	self.row += 1;
	}