Fix category panel loses focus after opened
When "AdwOverlaySplitView" opens the sidebar, it moves focus to the list
widget and the list widget *emits "row_selected" signal* with the
currently selected row. This quirks made the previously added
close-sidebar-on-row-select code to immediately close the sidebar upon
opening, but somehow the split view prevents closing the sidebar
immediately. As a result, the sidebar is closed-but-open state and focus
moves to the browse item row.
The code added in this patch is a workaround to this GTK bug. Inside
"row_selected" signal handler, it checks whether the signal is really a
"selected" event or not by testing the values.