Can't plant flower over existing flower.

game.go

@@ -163,6 +163,11 @@ func (g *Game) Load() {
 func (g *Game) Pause() { g.setSpeed(GameSpeedPaused) }
 
 func (g *Game) PlantFlower(id string, tile Point) {
+	if g.Terrain.HasFlower(tile) {
+		// TODO: notify user it tried to plant on tile with flower?
+		return
+	}
+
 	flower, ok := g.Herbarium.Find(id)
 	if !ok {
 		log.Println("user was able to plant a flower that doesn't exist")

map.go

@@ -24,6 +24,11 @@ func (m *Map) DigFlower(pos Point) string {
 	return flower.ID
 }
 
+func (m *Map) HasFlower(pos Point) bool {
+	_, ok := m.Flowers[pos]
+	return ok
+}
+
 func (m *Map) NewFlower(pos Point, id string, traits FlowerTraits) Flower {
 	flower := Flower{
 		ID:     id,