don't crash when concatenating structs with no fields * oct-map.cc (octave_map::cat (int, octave_idx_type, const octave_scalar_map*)): Quick return for N == 1. (octave_map::cat (int, octave_idx_type, const octave_map*)): Quick return for N == 1. Only call permute_to_correct_order if there are fields. Use dim_vector::concat to compute result dimensions if there are no fields. New tests for concatentation of structs with no fields. * pt-mat.cc (tm_const::init (const tree_matrix&)): Initialize all_1x1 to true if tree_matrix argument is not empty.

--- a/src/pt-mat.cc
+++ b/src/pt-mat.cc
@@ -546,7 +546,7 @@
   any_cell = false;
   any_sparse = false;
   any_class = false;
-  all_1x1 = ! empty ();
+  all_1x1 = ! tm.empty ();
 
   bool first_elem = true;
   bool first_elem_is_struct = false;