VP1Algs: fix for ATLASVPONE-673

As described in ATLASVPONE-673

I was getting the following error when opening ITK tracks in vp1:

ConditionStore                                    WARNING retrieve(non-const): No valid proxy for object PixelDetectorElementCollection  of type CondContBase(CLID 34480459) 
 Try to use a const retrieve
Exception: SG::ExcNoCondCont: Can't retrieve CondCont from ReadCondHandle for key ConditionStore+PixelDetectorElementCollection. Can't retrieve. (no backtrace available).
AthenaPoolConverter                                 ERROR createObj - caught exception: AthenaPoolCnvSvc::::ExcCaughtException: Caught exception in StatusCode T_AthenaPoolCustomCnvWithKey<TRANS, PERS>::PoolToDataObject(DataObject*&, const Token*, const std::string&) [with TRANS = DataVector<Trk::Track>; PERS = Trk::TrackCollection_tlp7; std::string = std::__cxx11::basic_string<char>] while creating transient objectDataVector<Trk::Track,DataModel_detail::NoBase>/CombinedMuonTracks: SG::ExcNoCondCont: SG::ExcNoCondCont: Can't retrieve CondCont from ReadCondHandle for key ConditionStore+PixelDetectorElementCollection. Can't retrieve.
AthenaPoolConverter                                 ERROR createObj failed to get DataObject, Token = [DB=218690EC-7A35-EC40-B30F-2EE92E0F85DD][CNT=CollectionTree(Trk::TrackCollection_tlp7/CombinedMuonTracks)][CLID=D8806153-CA92-4A1A-9859-68E40EB4E336][TECH=00000203][OID=0002B7020000007A-0002B70200000001]
DataProxy                                         WARNING accessData: conversion failed for data object 117682415/CombinedMuonTracks
 Returning NULL DataObject pointer  
VP1MESSAGE: 3DCocktail/Tracks: [VP1SGAccessHelper] ERROR: Failed StoreGateSvc::retrieve(..) with key=CombinedMuonTracks claimed to be succesful, but resulted in NULL pointer.

This MR fixes it (thanks to @tstreble for the suggestion)