fixing training zones with empty df bug

rowers/interactiveplots.py

@@ -6805,6 +6805,11 @@ def get_zones_report(rower,startdate,enddate,trainingzones='hr',date_agg='week',
 
 def interactive_zoneschart(rower,data,startdate,enddate,trainingzones='hr',date_agg='week',
                            yaxis='time'):
+    if startdate >= enddate:
+        st = startdate
+        startdate = enddate
+        enddate = st
+
     duration = enddate-startdate
 
     totaldays = duration.total_seconds()/(24*3600)
@@ -6866,6 +6871,8 @@ def interactive_zoneschart(rower,data,startdate,enddate,trainingzones='hr',date_
     df.sort_values('date_sorting',inplace=True)
     df.drop('date_sorting',inplace=True,axis='columns')
     df['totaltime']  = 0
+    if df.empty:
+        return '','No Data Found'
 
     if yaxis == 'percentage':
         dates = list(set(df['date'].values))