Keep previous `mousemove` event updated while zoompanning (closes #4155)
Keep previous `mousemove` event updated while zoompanning
(closes #4155)

ngageoint/hootenanny-ui,openstreetmap/iD,AndreasHae/iD,mapmeld/iD,digidem/iD,mapmeld/iD,openstreetmap/iD,bagage/iD,kartta-labs/iD,1ec5/iD,kartta-labs/iD,kartta-labs/iD,1ec5/iD,AndreasHae/iD,digidem/iD,ngageoint/hootenanny-ui,ngageoint/hootenanny-ui,AndreasHae/iD,bagage/iD,openstreetmap/iD,morray/iD,1ec5/iD,mapmeld/iD,morray/iD,bagage/iD