Blood: Avoid OOB access in MoveDude()

This trips UBSan in the beginning of the first level, including during the
first attract mode demo.

source/blood/src/actor.cpp

@@ -4456,7 +4456,7 @@ void MoveDude(spritetype *pSprite)
             spritetype *pHitSprite = &sprite[nHitSprite];
             XSPRITE *pHitXSprite = NULL;
             // Should be pHitSprite here
-            if (pSprite->extra > 0)
+            if (pSprite->extra > 0 && (unsigned)pHitSprite->extra < kMaxXSprites)
                 pHitXSprite = &xsprite[pHitSprite->extra];
             int nOwner = actSpriteOwnerToSpriteId(pHitSprite);