raise error in get_time if zero returned

Author: jerryneedell

adafruit_esp32spi/adafruit_esp32spi.py

@@ -766,6 +766,8 @@ def get_time(self):
         """The current unix timestamp"""
         if self.status == WL_CONNECTED:
             resp = self._send_command_get_response(_GET_TIME)
+            if struct.unpack('<i', resp[0]) == (0,):
+                raise ValueError("_GET_TIME returned 0")
             return struct.unpack('<i', resp[0])
         if self.status in (WL_AP_LISTENING, WL_AP_CONNECTED):
             raise RuntimeError("Cannot obtain NTP while in AP mode, must be connected to internet")