Properly remove SAO when worldedges are overtaken (#5889)

* LuaEntitySAO: Remove beyond outermost mapchunk edges

Based on a commit by, and with help from, nerzhul.
Add 2 functions to class Mapgen:
A function to calculate actual mapgen edges, called from the Mapgen constructor.
A function called indirectly from content_sao.cpp per entity step to check SAO
position is within mapgen edges.

* Calculate borders from params not mapgen, which is not available everytime

src/map.h

@@ -377,6 +377,8 @@ public:
 	*/
 	ServerMapSector *createSector(v2s16 p);
 
+	bool saoPositionOverLimit(const v3f &p);
+
 	/*
 		Blocks are generated by using these and makeBlock().
 	*/
@@ -409,9 +411,6 @@ public:
 	*/
 	MapBlock *getBlockOrEmerge(v3s16 p3d);
 
-	// Carries out any initialization necessary before block is sent
-	void prepareBlock(MapBlock *block);
-
 	// Helper for placing objects on ground level
 	s16 findGroundLevel(v2s16 p2d);