Avoid dividing by zero for sparkline in time table viz (#3679)
Avoid dividing by zero for sparkline in time table viz (#3679)


zhouyao1994/incubator-superset,mistercrunch/panoramix,apache/incubator-superset,timifasubaa/incubator-superset,alanmcruickshank/superset-dev,airbnb/caravel,zhouyao1994/incubator-superset,apache/incubator-superset,airbnb/superset,alanmcruickshank/superset-dev,airbnb/superset,dmigo/incubator-superset,airbnb/superset,zhouyao1994/incubator-superset,apache/incubator-superset,timifasubaa/incubator-superset,zhouyao1994/incubator-superset,timifasubaa/incubator-superset,airbnb/caravel,mistercrunch/panoramix,mistercrunch/panoramix,mistercrunch/panoramix,airbnb/superset,timifasubaa/incubator-superset,zhouyao1994/incubator-superset,dmigo/incubator-superset,apache/incubator-superset,alanmcruickshank/superset-dev,airbnb/caravel,dmigo/incubator-superset,alanmcruickshank/superset-dev,apache/incubator-superset,dmigo/incubator-superset,airbnb/caravel