fix bug where track narrowing would leave the scroll position lower than it should be
fix bug where track narrowing would leave the scroll position lower than it should be

nathandunn/jbrowse,GreggHelt2/apollo-test,Arabidopsis-Information-Portal/jbrowse,nathandunn/jbrowse,Arabidopsis-Information-Portal/jbrowse,igemsoftware/Shenzhen_BGIC_0101_2013,limeng12/jbrowse,Arabidopsis-Information-Portal/jbrowse,GMOD/jbrowse,erasche/jbrowse,SuLab/jbrowse,nathandunn/jbrowse,GreggHelt2/apollo-test,igemsoftware/Shenzhen_BGIC_0101_2013,GreggHelt2/apollo-test,erasche/jbrowse,erasche/jbrowse,GreggHelt2/apollo-test,Arabidopsis-Information-Portal/jbrowse,GMOD/jbrowse,erasche/jbrowse,igemsoftware/Shenzhen_BGIC_0101_2013,igemsoftware/Shenzhen_BGIC_0101_2013,SuLab/jbrowse,limeng12/jbrowse,Arabidopsis-Information-Portal/jbrowse,GMOD/jbrowse,erasche/jbrowse,SuLab/jbrowse,igemsoftware/Shenzhen_BGIC_0101_2013,SuLab/jbrowse,igemsoftware/Shenzhen_BGIC_0101_2013,GMOD/jbrowse,erasche/jbrowse,GreggHelt2/apollo-test,GMOD/jbrowse,Arabidopsis-Information-Portal/jbrowse,nathandunn/jbrowse,limeng12/jbrowse,erasche/jbrowse,SuLab/jbrowse,limeng12/jbrowse,nathandunn/jbrowse,limeng12/jbrowse,igemsoftware/Shenzhen_BGIC_0101_2013,SuLab/jbrowse,erasche/jbrowse,limeng12/jbrowse,limeng12/jbrowse,Arabidopsis-Information-Portal/jbrowse,SuLab/jbrowse,GreggHelt2/apollo-test,limeng12/jbrowse,igemsoftware/Shenzhen_BGIC_0101_2013,GreggHelt2/apollo-test