TrayViewport: handle the case of the widget not yet allocated in the size-allocate callback - SL #4279
TrayViewport: handle the case of the widget not yet allocated in the size-allocate callback - SL #4279

In the callback, the allocation can be 1x1 if it is yet unknown [1].
This is the case of trays that start hidden by default, like the one
in Browse activity.

[1] http://developer.gnome.org/gtk3/stable/GtkWidget.html#gtk-widget-size-allocate

Signed-off-by: Manuel Kaufmann <54d769c38f2aa6d2679b577ce2986fc3d1abeaba@gmail.com>
Signed-off-by: Manuel Quiñones <6f5069c5b6be23302a13accec56587944be09079@laptop.org>
Acked-by: Simon Schampijer <088e16a1019277b15d58faf0541e11910eb756f6@laptop.org>

quozl/sugar-toolkit-gtk3,samdroid-apps/sugar-toolkit-gtk3,puneetgkaur/backup_sugar_sugartoolkit,manuq/sugar-toolkit-gtk3,Daksh/sugar-toolkit-gtk3,quozl/sugar-toolkit-gtk3,manuq/sugar-toolkit-gtk3,i5o/sugar-toolkit-gtk3,Daksh/sugar-toolkit-gtk3,quozl/sugar-toolkit-gtk3,sugarlabs/sugar-toolkit-gtk3,puneetgkaur/sugar-toolkit-gtk3,sugarlabs/sugar-toolkit-gtk3,Daksh/sugar-toolkit-gtk3,samdroid-apps/sugar-toolkit-gtk3,i5o/sugar-toolkit-gtk3,godiard/sugar-toolkit-gtk3,quozl/sugar-toolkit-gtk3,godiard/sugar-toolkit-gtk3,i5o/sugar-toolkit-gtk3,puneetgkaur/sugar-toolkit-gtk3,manuq/sugar-toolkit-gtk3,i5o/sugar-toolkit-gtk3,ceibal-tatu/sugar-toolkit-gtk3,godiard/sugar-toolkit-gtk3,puneetgkaur/backup_sugar_sugartoolkit,tchx84/debian-pkg-sugar-toolkit-gtk3,sugarlabs/sugar-toolkit-gtk3,samdroid-apps/sugar-toolkit-gtk3,ceibal-tatu/sugar-toolkit-gtk3,tchx84/sugar-toolkit-gtk3,tchx84/sugar-toolkit-gtk3,tchx84/debian-pkg-sugar-toolkit-gtk3,puneetgkaur/backup_sugar_sugartoolkit,samdroid-apps/sugar-toolkit-gtk3,tchx84/sugar-toolkit-gtk3,tchx84/debian-pkg-sugar-toolkit-gtk3,ceibal-tatu/sugar-toolkit-gtk3,puneetgkaur/sugar-toolkit-gtk3