Fix concatenation of a struct with an empty cell array (bug #39041) * pt-tm-const.cc (tm_row_const::tm_row_const_rep::do_init_element): Don't ignore empty cell array that occurs first in a row vector, allow structs to convert properly. * data.cc, pt-mat.cc: Add BIST tests for this fix. Add failing tests for a similar compatibility bug.

--- a/libinterp/parse-tree/pt-tm-const.cc	Sun May 21 18:03:58 2017 -0700
+++ b/libinterp/parse-tree/pt-tm-const.cc	Mon May 22 12:12:45 2017 -0700
@@ -82,6 +82,8 @@
             first_elem = false;
           }
       }
+    else if (val.is_cell ())
+      first_elem = false;
 
     append (val);