Fix syntax error for URIQualifiedName followed by a colon

[GuntherRademacher]

As reported by Andrew Sales on basex-talk, a URIQualifiedName without the optional prefix raised a syntax error when immediately followed by a colon (e.g. the := operator) with no intervening whitespace, as in:

let $Q{}foo:=1 return $Q{}foo

When parsing an EQName, QueryParser.eQName speculatively consumes a : to check for the optional-prefix form Q{uri}prefix:local (qtspecs#2227). When no valid local name follows, the colon was not given back, so the surrounding := could no longer be recognized. The parser now restores its position in that case.

[ChristianGruen]

A literal hotfix… and a new snapshot.