Visual Style Editor filter button is active even if all the filter rules have been cleared

[allyoucanmap]

Steps to reproduce:

• open a layer in geonode
• select edit style
• select a style to edit and open the visual style editor
• click on the filter button to apply a filter
• close the popup with the filter applied
• now the button is active
• open the filter popup again and clear all the filters
• close the popup

Expected Result:

• the filter button is not active anymore

Current Result:

• the filter button is active

Note: This is an issue related to MapStore submodule

[simboss]

@tdipisa let's schedule this fix for next release