error catching around interval parser

rowers/views.py

@@ -7383,7 +7383,10 @@ def workout_summary_edit_view(request,id,message="",successmessage=""
 	if form.is_valid():
 	    cd = form.cleaned_data
 	    s = cd["intervalstring"]
-	    rowdata.updateinterval_string(s)
+            try:
+	        rowdata.updateinterval_string(s)
+            except IndexError:
+                messages.error(request,'Interval string parse error')
 	    intervalstats = rowdata.allstats()
 	    itime,idist,itype = rowdata.intervalstats_values()
 	    nrintervals = len(idist)