Fix opacity on notification hover
Based on the results from git bisect the regression has been introduced by the commit 79ac9cab.
On notification hover the opacity is correctly set to 1 (xfce4-notifyd/xfce-notify-window.c:945), but is immediately overridden with the preset value (xfce4-notifyd/xfce-notify-window.c:1109) in the function which is called from motion notify event handler (xfce4-notifyd/xfce-notify-window.c:941).
Fixes #119 (closed)