bitbake: server/process: Don't send heartbeats when no idle functions

If there are no idle functions present, don't sent heartbeat events. These
are only meant to happen while builds are active.

(Bitbake rev: 9a2d5e63b07c3912838781776c61f0f1ac9640e1)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/lib/bb/server/process.py

@@ -477,7 +477,7 @@ class ProcessServer():
 
             # Create new heartbeat event?
             now = time.time()
-            if bb.event._heartbeat_enabled and now >= self.next_heartbeat:
+            if items and bb.event._heartbeat_enabled and now >= self.next_heartbeat:
                 # We might have missed heartbeats. Just trigger once in
                 # that case and continue after the usual delay.
                 self.next_heartbeat += self.heartbeat_seconds