prevent users to use 0 as planned session value

rowers/models.py

@@ -1764,6 +1764,9 @@ class PlannedSession(models.Model):
 	return stri
 
     def save(self, *args, **kwargs):
+        if self.sessionvalue <= 0:
+            self.sessionvalue = 1
+        
         # sort units
         if self.sessionmode == 'distance':
             if self.sessionunit not in ['m','km']:
@@ -2005,6 +2008,14 @@ class IndoorVirtualRaceForm(ModelForm):
         cd = self.cleaned_data
         timezone_str = cd['timezone']
 
+        value = cd['sessionvalue']
+        if value <= 0:
+            raise forms.ValidationError('The Value must be a positive, non-zero value')
+
+        unit = cd['sessionunit']
+        if unit == 'm' and value < 100:
+            raise forms.ValidationError('Minimum distance is 100m')
+        
         start_time = cd['start_time']
         if start_time is None:
             raise forms.ValidationError(