Bug fix to restore preservation and display of recently-used filters

I inadvertently broke this - when you place focus in the display filter
widget, with an empty field, the drop-down should be populated with the
list of most-recently-used filters, like Wireshark. Instead, I wasn't
saving these filters, so the list to display was always empty - in that
case, termshark falls back to show filter tokens whose prefix matches
the current field value (which is empty).

ui/ui.go

@@ -2813,6 +2813,7 @@ func RequestLoadPcap(pcapf string, displayFilter string, jump termshark.GlobalJu
 func RequestNewFilter(displayFilter string, app gowid.IApp) {
 	handlers := pcap.HandlerList{
 		SimpleErrors{},
+		MakeSaveRecents("", displayFilter),
 		MakePacketViewUpdater(),
 		MakeUpdateCurrentCaptureInTitle(),
 		SetStructWidgets{Loader}, // for OnClear