Bug#30832:Assertion + crash with select name_const('test',now());

Completion of previous patch. Negative number were denied
as the second argument to NAME_CONST.

mysql-test/r/func_misc.result

@@ -195,9 +195,15 @@ NULL
 SELECT NAME_CONST('test', 1);
 test
 1
+SELECT NAME_CONST('test', -1);
+test
+-1
 SELECT NAME_CONST('test', 1.0);
 test
 1.0
+SELECT NAME_CONST('test', -1.0);
+test
+-1.0
 SELECT NAME_CONST('test', 'test');
 test
 test

mysql-test/t/func_misc.test

@@ -199,7 +199,9 @@ SELECT NAME_CONST('test', UPPER('test'));
 
 SELECT NAME_CONST('test', NULL);
 SELECT NAME_CONST('test', 1);
+SELECT NAME_CONST('test', -1);
 SELECT NAME_CONST('test', 1.0);
+SELECT NAME_CONST('test', -1.0);
 SELECT NAME_CONST('test', 'test');
 
 --echo End of 5.0 tests

sql/item_func.h

@@ -435,6 +435,7 @@ class Item_func_neg :public Item_func_num1
   longlong int_op();
   my_decimal *decimal_op(my_decimal *);
   const char *func_name() const { return "-"; }
+  virtual bool basic_const_item() const { return args[0]->basic_const_item(); }
   void fix_length_and_dec();
   void fix_num_length_and_dec();
   uint decimal_precision() const { return args[0]->decimal_precision(); }