Also skip flattening zero-sized arrays

when converting to SMT2 queries.

Author: petr-bauch

Diff for: src/solvers/smt2/smt2_conv.cpp

@@ -2695,8 +2695,8 @@ void smt2_convt::flatten_array(const exprt &expr)
   PRECONDITION(size_expr.id() == ID_constant);
 
   mp_integer size = numeric_cast_v<mp_integer>(to_constant_expr(size_expr));
-  CHECK_RETURN_WITH_DIAGNOSTICS(size != 0, "can't convert zero-sized array");
-
+  if(size == 0)
+    return;
   out << "(let ((?far ";
   convert_expr(expr);
   out << ")) ";