Update GetDataHandlers.cs

Attempt to correct Celestial Sigil not functioning #1065 (https://github.com/NyxStudios/TShock/issues/1065). It seems to work well.

TShockAPI/GetDataHandlers.cs

@@ -3560,6 +3560,7 @@ namespace TShockAPI
 					case -5:
                     case -6:
                     case -7:
+        				case -8:
 						invasion = true;
 						break;
                     case 4:
@@ -3607,6 +3608,9 @@ namespace TShockAPI
 			string boss;
 			switch (Type)
 			{
+				case -8:
+					boss = "a Moon Lord";
+					break;
 				case -7:
 					boss = "a Martian invasion";
 					break;