Catch GrpcError in new example

Apparently, it was a little _too_ simple.

Also, update the description for seconds_to_first_nonempty_slot field to reflect some behavior this script was able to capture.

poll_history.py

@@ -25,6 +25,7 @@ def run_loop(context):
     counter = None
     prev_triggered = False
     while True:
+        try:
             # `starlink_grpc.status_data` returns a tuple of 3 dicts, but in case
             # the API changes to add more in the future, it's best to reference
             # them by index instead of direct assignment from the function call.
@@ -34,7 +35,11 @@ def run_loop(context):
             # On the other hand, `starlink_grpc.history_bulk_data` will always
             # return 2 dicts, because that's all the data there is.
             general, bulk = starlink_grpc.history_bulk_data(samples, start=counter, context=context)
-
+        except starlink_grpc.GrpcError:
+            # Dish rebooting maybe, or LAN connectivity error. Just ignore it
+            # and hope it goes away.
+            pass
+        else:
             # The following is what actually does stuff with the data. It should
             # be replaced with something more useful.
 
@@ -45,7 +50,8 @@ def run_loop(context):
             # This computes a trigger detecting samples not marked as scheduled:
             triggered = not all(bulk["scheduled"])
             if triggered or prev_triggered:
-            print("Triggered" if triggered else "Continued", "at:", datetime.now(tz=timezone.utc))
+                print("Triggered" if triggered else "Continued", "at:",
+                      datetime.now(tz=timezone.utc))
                 print("status:", status)
                 print("history:", bulk)
                 if not triggered:

starlink_grpc.py

@@ -39,7 +39,10 @@ This group holds information about the current state of the user terminal.
 : **snr** : Most recent sample value. See bulk history data for detail.
 : **seconds_to_first_nonempty_slot** : Amount of time from now, in seconds,
     until a satellite will be scheduled to be available for transmit/receive.
-    See also *scheduled* in the bulk history data.
+    See also *scheduled* in the bulk history data. May report as a negative
+    number, which appears to indicate unknown time until next satellite
+    scheduled and usually correlates with *state* reporting as other than
+    "CONNECTED".
 : **pop_ping_drop_rate** : Most recent sample value. See bulk history data for
     detail.
 : **downlink_throughput_bps** : Most recent sample value. See bulk history