added spawning rule to mooshroom

src/MobSpawner.cpp

@@ -285,6 +285,19 @@ bool cMobSpawner::CanSpawnHere(cChunk * a_Chunk, int a_RelX, int a_RelY, int a_R
 					)
 				);
 			}
+
+			case mtMooshroom:
+			{
+				return (
+					(TargetBlock == E_BLOCK_AIR) &&
+					(BlockAbove == E_BLOCK_AIR) &&
+					(!cBlockInfo::IsTransparent(BlockBelow)) &&
+					(
+						a_Biome == biMushroomShore ||
+						a_Biome == biMushroomIsland
+					)
+				);
+			}
 			
 			default:
 			{