Use simple GtkBox widgets instead.
GtkTable does not support nth-child() constructs for CSS, so the theme
is not able to match the inline toolbar with selectors like
.inline-toolabr.toolbar:nth-child(last) {
}
which are used to change the rounded corners/top border width.
https://bugzilla.gnome.org/show_bug.cgi?id=658964
When bailing out early, the cleanup path is unreffing the provider
because the variable was used in the loop. We need to set it back
to NULL there.
https://bugzilla.gnome.org/show_bug.cgi?id=657819
