Merge pull request #17 from jerryneedell/jerryn_None

Fix potential first read issue

Author: tannewt

adafruit_dht.py

@@ -138,7 +138,11 @@ def measure(self):
         delay_between_readings = 0.5
         if self._dht11:
             delay_between_readings = 1.0
-        if time.monotonic()-self._last_called > delay_between_readings:
+        # Initiate new reading if this is the first call or if sufficient delay
+        # If delay not sufficient - return previous reading.
+        # This allows back to back access for temperature and humidity for same reading
+        if (self._last_called == 0 or
+                (time.monotonic()-self._last_called) > delay_between_readings):
             self._last_called = time.monotonic()
 
             pulses = self._get_pulses()