use prefab CoPOffset instead

Given stock code, this should always be 0 for everything except parts with ModuleProceduralFairing.  But if some mod poked a different value into the prefab, this should be more correct.  And if a mod poked a different module into the part instance, then we're kinda screwed anyway.

Author: JonnyOThan

Source/Modules/ModuleCoPFollowTransform.cs

@@ -26,10 +26,11 @@ public override void OnLoad(ConfigNode node)
                 if (followTransform == null) Debug.LogError($"[{MODULENAME}] transformName '{transformName}' was empty or does not exist on part '{part.partInfo?.name}'");
             }
 
-            if (followTransform == null)
+            if (followTransform == null && part.partInfo != null)
             {
                 // this may be important if someone is swapping out versions of this module with B9PS
-                part.CoPOffset = Vector3.zero;
+                // Note this probably isn't correct for parts that also have modules that mess with this field (e.g. ModuleProceduralFairing)
+                part.CoPOffset = part.partInfo.CoPOffset;
             }
 
             // NOTE: isEnabled will be persisted to the save file, but we want to treat it purely as runtime state