Stop expand if no more places for expanding
It complained "AttributeError: 'NoneType' object has no attribute 'rounded'" when my bot take every available places to build  main bases.  In that case, the location got from `get_next_expansion` will be None and cause the error.
@@ -142,6 +142,7 @@ class BotAI:
if not location:
location = await self.get_next_expansion()
+ if location:
await self.build(building, near=location, max_distance=max_distance, random_alternative=False, placement_step=1)
async def get_next_expansion(self) -> Optional[Point2]:
@@ -413,6 +414,8 @@ class BotAI:
near = near.position.to2
elif near is not None:
near = near.to2
+ else:
+ return
p = await self.find_placement(building, near.rounded, max_distance, random_alternative, placement_step)
if p is None:
