[solar2d] Closes #1749, check if removeSelf is available on draw group

.gitignore

@@ -108,8 +108,7 @@ spine-tk2d/*.sln
 spine-tk2d/Assets/TK2DROOT*
 spine-tk2d/Assets/-tk2d*
 
-spine-corona/spine-lua/
-!spine-corona/spine-lua/Place spine-lua here.txt
+spine-solar2d/spine-lua/
 
 spine-love/spine-lua/
 spine-love/love/

spine-solar2d/spine-solar2d/spine.lua

@@ -133,7 +133,7 @@ function spine.Skeleton:updateWorldTransform()
 	if (self.vertexEffect) then self.vertexEffect:beginEffect(self) end
 
 	-- Remove old drawing group, we will start anew
-	if self.drawingGroup then self.drawingGroup:removeSelf() end
+	if self.drawingGroup and self.drawingGroup.removeSelf then self.drawingGroup:removeSelf() end
 	local drawingGroup = display.newGroup()
 	self.drawingGroup = drawingGroup
 	self.group:insert(drawingGroup)