Supplement a default value in case the frame for whatever reason does not have a top point

diff --git a/BonusRollPreview.lua b/BonusRollPreview.lua
index 67accc4..3680d14 100644
--- a/BonusRollPreview.lua
+++ b/BonusRollPreview.lua
@@ -92,7 +92,7 @@ local function HookStartRoll(self, frame)
 end

 local function PositionDownwards()
-	return (GetScreenHeight() - BonusRollFrame:GetTop()) < 345
+	return (GetScreenHeight() - (BonusRollFrame:GetTop() or 200)) < 345
 end

 local collapsed