better empower detection in physics calc

rowers/tasks.py

@@ -164,10 +164,11 @@ def handle_otwsetpower(f1,boattype,weightvalue,
     powermeasured = False
     try:
         w = rowdata.df['wash']
-        powermeasured = True
+        if w.mean() != 0:
+            powermeasured = True
     except KeyError:
         pass
-        
+
     rowdata.otw_setpower_silent(skiprows=5,mc=weightvalue,rg=rg,
                                 powermeasured=powermeasured)