[server] Fix BBOX SRS in WFS GetFeature POST with two queries

[arnaud-morvan]

Description

Correctly transform featureRequest.filterRect in WFS POST GetFeature request with multiple Query elements.

Checklist

Reviewing is a process done by project maintainers, mostly on a volunteer basis. We try to keep the overhead as small as possible and appreciate if you help us to do so by completing the following items. Feel free to ask in a comment if you have troubles with any of them.

• Commit messages are descriptive and explain the rationale for changes
• Commits which fix bugs include fixes #11111 in the commit message next to the description
• Commits which add new features are tagged with [FEATURE] in the commit message
• Commits which change the UI or existing user workflows are tagged with [needs-docs] in the commit message and contain sufficient information in the commit message to be documented
• I have read the QGIS Coding Standards and this PR complies with them
• This PR passes all existing unit tests (test results will be reported by travis-ci after opening this PR)
• New unit tests have been added for core changes
• I have run the scripts/prepare-commit.sh script before each commit

[arnaud-morvan]

@rldhont @pblottiere : Another SRS fix in WFS GetFeature.

[arnaud-morvan]

@rldhont : Thanks for review.
I think this is ready for merge, but I do not have push rights (no merge button on my side).

[arnaud-morvan]

How about merging this server fix ?

[arnaud-morvan]

Thanks :)