Applied bug fix from trunk r1646966
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Applied patch from jira issue OFBIZ-5385 - Purchase order immutable/unchangeable errors when adding variant products.
Thanks Christian for reporting the issue. Thanks Arun for providing the patch.
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git-svn-id: https://svn.apache.org/repos/asf/ofbiz/branches/release13.07@1646973 13f79535-47bb-0310-9956-ffa450edef68