Decimal place inconsistency occurs in the Top Hosts widget when using the 'avg' aggregation.

When using MySQL DB, 4 digits after comma are displayed, but with PostgreSQL, a lot more digits are displayed after comma. 

Steps to reproduce:

Conditions : PostgreSQL database.

1. Create a host
2. Add Zabbix trapper item to this host, item type - Numeric(unsigned).
3. Send any value to the item.
4. Create a top hosts widget:
   1. add a column with created item
   2. add aggregation function 'avg' to this column.
5. Save the widget and observe that when you hover over the result in the top hosts widget, approximately 20 digits are shown after the decimal point in the hintbox:

Note: This issue cannot be reproduced, if MySQL database is used.