[sndvol32] the dialog becomes huge in y after deselecting a channel

Reproduction steps
-Run sndvol32 of ros 0.4.12-dev-694-g0dd4b35 on XPSP3
-you will see something like 1sndvol32.PNG
-click "options" from menubar and select "properties" from dropdown-dlg
-deselect an arbitrary channel and confirm with "ok" button

Expected result
The channel is not longer displayed and the dialog should not change its y dimension

Observed result
The channel is not longer displayed but the dialog erroneously becomes huge in y
2sndvol.PNG