Allow empty sparse matrix inputs to qr() (bug #63069) * qr.cc (Fqr): Add BIST tests for bug #63069. * sparse-qr.cc (sparse_qr<SparseMatrix>::sparse_qr_rep::sparse_qr_rep, sparse_qr<SparseMatrix>::sparse_qr_rep::C, sparse_qr<SparseMatrix>::sparse_qr_rep::tall_solve<MArray<double>, Matrix>, sparse_qr<SparseComplexMatrix>::sparse_qr_rep::sparse_qr_rep, sparse_qr<SparseComplexMatrix>::sparse_qr_rep::C, sparse_qr<SPARSE_T>::solve): Change input validation from "<= 0" to "< 0". Change error message to "matrix dimension with negative size" from "matrix dimension with negative or zero size".