Bug#49489: Uninitialized cache led to a wrong result.

Arg_comparator uses Item_cache objects to store constants being compared when
they're need a type conversion. Because this cache wasn't initialized properly
Arg_comparator might produce wrong comparison result.

The Arg_comparator::cache_converted_constant function now initializes cache
prior to usage.

mysql-test/r/select.result:
  Added a test case for he bug#49489.
mysql-test/t/select.test:
  Added a test case for he bug#49489.
sql/item_cmpfunc.cc:
  Bug#49489: Uninitialized cache led to a wrong result.
  The Arg_comparator::cache_converted_constant function now initializes cache
  prior to usage.

mysql-test/r/select.result

@@ -4609,4 +4609,14 @@ HAVING v <= 't'
 ORDER BY pk;
 v
 DROP TABLE t1;
+#
+# Bug#49489 Uninitialized cache led to a wrong result.
+#
+CREATE TABLE t1(c1 DOUBLE(5,4));
+INSERT INTO t1 VALUES (9.1234);
+SELECT * FROM t1 WHERE c1 < 9.12345;
+c1
+9.1234
+DROP TABLE t1;
+# End of test for bug#49489.
 End of 5.1 tests

mysql-test/t/select.test

@@ -3964,4 +3964,13 @@ ORDER BY pk;
 
 DROP TABLE t1;
 
+--echo #
+--echo # Bug#49489 Uninitialized cache led to a wrong result.
+--echo #
+CREATE TABLE t1(c1 DOUBLE(5,4));
+INSERT INTO t1 VALUES (9.1234);
+SELECT * FROM t1 WHERE c1 < 9.12345;
+DROP TABLE t1;
+--echo # End of test for bug#49489.
+
 --echo End of 5.1 tests

sql/item_cmpfunc.cc

@@ -1023,7 +1023,7 @@ Item** Arg_comparator::cache_converted_constant(THD *thd, Item **value,
       (*value)->const_item() && type != (*value)->result_type())
   {
     Item_cache *cache= Item_cache::get_cache(*value, type);
-    cache->store(*value);
+    cache->setup(*value);
     *cache_item= cache;
     return cache_item;
   }