issues about clicking 'cancel' button in Buffer panel

[liuar]

steps:

1. view a flexible web layout
   
2. click 'Buffer' button, so system open the buffer editor panel
   
3. user select an area in the map
   
4. click 'Cancel' button in the buffer panel
   

result:
system just clear the selection in the map, but the buffer editor panel is still dislayed and the 'Done' buttion is still enabled. so that user may go on to click 'Done', which results in error

[liuar]

expected result:
when user clicks 'Cancel' button in the buffere panel, it's better to close the buffer panel

[liuar]

Disable the Done button while user clicks the cancel is a proper solution.

[liuar]

Changeset [2276] by liuar