nir/glsl_to_nir: ignore an instruction's dest if it hasn't any

Reviewed-by: Connor Abbott <connor.w.abbott@intel.com>
Reviewed-by: Kristian Høgsberg <krh@bitplanet.net>

src/glsl/nir/glsl_to_nir.cpp

@@ -1036,7 +1036,8 @@ nir_visitor::add_instr(nir_instr *instr, unsigned num_components)
 {
    nir_dest *dest = get_instr_dest(instr);
 
-   nir_ssa_dest_init(instr, dest, num_components, NULL);
+   if (dest)
+      nir_ssa_dest_init(instr, dest, num_components, NULL);
 
    nir_instr_insert_after_cf_list(this->cf_node_list, instr);
    this->result = instr;