correct (finally) condition for MATCH >0, >=0 etc in add_ft_keys (SW#1647)

still no rec. descent

sql/sql_select.cc

@@ -1655,17 +1655,17 @@ add_ft_keys(DYNAMIC_ARRAY *keyuse_array,
     {
       Item_func *arg0=(Item_func *)(func->arguments()[0]),
                 *arg1=(Item_func *)(func->arguments()[1]);
-      if ((functype == Item_func::GE_FUNC ||
-           functype == Item_func::GT_FUNC)  &&
-           arg0->type() == Item::FUNC_ITEM          &&
-           arg0->functype() == Item_func::FT_FUNC   &&
-           arg1->const_item() && arg1->val()>0)
+      if (arg1->const_item()  &&
+          ((functype == Item_func::GE_FUNC && arg1->val()> 0) ||
+           (functype == Item_func::GT_FUNC && arg1->val()>=0))  &&
+           arg0->type() == Item::FUNC_ITEM            &&
+           arg0->functype() == Item_func::FT_FUNC)
         cond_func=(Item_func_match *) arg0;
-      else if ((functype == Item_func::LE_FUNC ||
-                functype == Item_func::LT_FUNC)  &&
+      else if (arg0->const_item() &&
+               ((functype == Item_func::LE_FUNC && arg0->val()> 0) ||
+                (functype == Item_func::LT_FUNC && arg0->val()>=0)) &&
                 arg1->type() == Item::FUNC_ITEM          &&
-                arg1->functype() == Item_func::FT_FUNC   &&
-                arg0->const_item() && arg0->val()>0)
+                arg1->functype() == Item_func::FT_FUNC)
         cond_func=(Item_func_match *) arg1;
     }
   }