glsl2: Add missing sig_iter.next() to the no-constant-folding-to-outvals fix.

src/glsl/ir_constant_folding.cpp

@@ -117,6 +117,7 @@ ir_constant_folding_visitor::visit_enter(ir_call *ir)
 	    param_rval->replace_with(new_param);
 	 }
       }
+      sig_iter.next();
    }
 
    return visit_continue_with_parent;

src/glsl/ir_tree_grafting.cpp

@@ -202,6 +202,7 @@ ir_tree_grafting_visitor::visit_enter(ir_call *ir)
 	 ir->replace_with(new_ir);
 	 return visit_stop;
       }
+      sig_iter.next();
    }
 
    return visit_continue;