[Backport 7.9] From repository servlet, trim the xpath/sql query param before encoding

I've now been bitten multiple times by a copy-paste query into the repository servlet that looks for example like

//*[@hippo:availability]

which does not return any result and does not give any exception. Typically after debugging, I finally find the leading space being the culprit.

Note the 7.8 these queries did return results