accounted for possible 'notgzip' response from rowingdata

rowers/dataprep.py

@@ -866,6 +866,13 @@ def new_workout_from_file(r,f2,
         os.remove(f2)
         message = "It looks like this file doesn't contain stroke data."
         return (0,message,f2)
+
+    # Some people upload corrupted zip files
+    if fileformat == 'notgzip':
+        os.remove(f2)
+        message = "Rowsandall could not process this file. The extension is supported but the file seems corrupt. Contact info@rowsandall.com if you think this is incorrect."
+        return (0,message,f2)
+
     
     # Some people try to upload RowPro summary logs
     if fileformat == 'rowprolog':