Hardening/523

Fix issue #523 

This PR goes only to develop branch (as it is a fix for a functionality included only in develop)
The explanation is provided in a comment in PR #515:

> I understand that, after last changes in the code, the forwarded updateContextRequest contains only one element, which is "filled" here:
>
>```
>ucrP->contextElementVector.push_back(ceP);
>ceP->fill(upcr.contextElementResponseVector[ix]->contextElement);
>```
>
>Thus, the updateContextElementResponse (stored in `provUpcrsP`) should contain only one >element, a 0-th position. Using `ix` here could cause at out of range segfault in the case of ix !=0.
>
>In sum, I think we should use here:
>
>```
>cerP->contextElement.fill(provUpcrsP->contextElementResponseVector[0]->contextElement);
>cerP->statusCode.fill(&provUpcrsP->contextElementResponseVector[0]->statusCode);
>```