Match Matlab return dimensions for find on empty sparse matrices (bug #42408). * find.cc (find_nonzero_elem_idx (const Sparse<T>& v)): Match Matlab return dimensions for odd cases such as 0x1, 1x0, 1x1(empty) sparse matrices. The conditions are documented in Array.cc (Array<T>::find) and are already implemented for other array types besides sparse. * find.cc (find_nonzero_elem_idx (const PermMatrix& v)): Match Matlab return dimensions for odd cases such as 0x1, 1x0, 1x1(empty) permutation matrices.