GtkScrolledWindow in GTK 3.16 might have a minimum and natural height
of 0 if GTK_OVERLAY_SCROLLING is enabled (which is the default), so we
need to fix our overridden minimal height to never be greater than the
natural height.

Do that by only changing the minimal height if it is greater than what
we want.

I don't know why we didn't use to set 0 here, but it might be that a
height of 0 caused problems on older GTK versions, so keep 1 to be sure.

X-Scintilla-Commit-ID: e9f9c964236a6b740f75d09a8b0ac76e5d6dd09f