Problem description:
Graph widget draws negative values incorrectly in case if field Draw is set to Bar - an offset that is equal to the length of the bar is observed in respect to the x axis:

Steps to reproduce:

1. Create a host with a trapper item (float)
2. Open any dashboard and add an svg graph widget that displays the previously created item.
   Important: set Draw = Bar
3. Send both negative and positive values to the trapper item
4. Check how data is displayed on the graph widget

Result: negative values have an offset in respect to the x axis that is equal to their height (bar starts at point where is should end)
Expected: bars should start at y=0 level.