Fix for issue markruys#8

It appears that GetPowerStationPowerAndIncomeByDay returns figures for multiple dates.
Hence this "fix" in order to ensure that the correct one is taken into account.
The code could probably be cleaner but knowing that it is not 100% sur how the GoodWe API works, it is robust as such.

gw2pvo/gw_api.py

@@ -79,6 +79,13 @@ def getDayReadings(self, date):
             return result
 
         eday_kwh = data[0]['p']
+
+        # added a loop  to select correct day in case the GoodWe API unexpectedly returns figures for multiple dates
+        if len(data) > 1:
+            date_s_expected = date.strftime("%m/%d/%Y")
+            for idata in data:
+                  if(idata['d'] == date_s_expected):
+                      eday_kwh = idata['p']                
 
         payload = {
             'id' : self.system_id,