Fix parsing POSTed WFS XMLrequest: srsName attribute  is on Query, not on GetFeature

In msWFSParseRequest (mapwfs.c), when parsing not using LIBXML2 then for the GetFeature request the srsName attribute is currently looked for on the GetFeature element (and therefore never found) and not on the Query element.

This change fixes that so that Query@srsName is checked.