Fix potential blender crash during export.

Blender can crash during export when baking vertex colors to shared mesh
data objects. Doing that can lead to lighting gotchas, but it's better
to have lighting gotchas than crashes.

korman/exporter/etlight.py

@@ -375,12 +375,9 @@ class LightBaker(_MeshManager):
         if not self._generate_lightgroup(bo, user_lg):
             return False
 
-        # I have heard tale of some moar "No valid image to bake to" boogs if there is a really
-        # old copy of the autocolor layer on the mesh. Nuke it.
         autocolor = vcols.get("autocolor")
-        if autocolor is not None:
-            vcols.remove(autocolor)
-        autocolor = vcols.new("autocolor")
+        if autocolor is None:
+            autocolor = vcols.new("autocolor")
         toggle.track(vcols, "active", autocolor)
 
         # Mark "autocolor" as our active render layer