Fix sporadic crash on startup - seen on termux

panic: runtime error: index out of range [7] with length 7 goroutine 1 [running]:
github.com/gcla/termshark/v2/ui.makePacketListModel(0x60602f78 98,
0x400028a6a8, 0x6060300838, 0x4003de68f0, 0x40003b1fe0)
/home/builder/.termux-build/termshark/src/ui/ui.go:2289
github.com/gcla/termshark/v2/ui.updatePacketListWithData (0x60602f7898, 0x400028a6a8, 0x6060300838, 0x4003de68f0)
/home/builder/.termux-build/termshark/src/ui/ui.go:230

ui/ui.go

@@ -2290,7 +2290,7 @@ func makePacketListModel(psml psmlInfo, app gowid.IApp) *psmlmodel.Model {
 
 	if len(expandingModel.Comparators) > 0 {
 		for i, _ := range expandingModel.Comparators {
-			if i < len(widths) {
+			if i < len(widths) && i < len(cols) {
 				if field, ok := shark.AllowedColumnFormats[cols[i].Field.Token]; ok {
 					if field.Comparator != nil {
 						expandingModel.Comparators[i] = field.Comparator