If a line is filtered while printing, read next line to continue sending

We want to make sure that while printing we always continue sending something,
either from the command queue or the printed file.

src/octoprint/util/comm.py

@@ -332,6 +332,10 @@ class MachineCom(object):
 	def __del__(self):
 		self.close()
 
+	@property
+	def _active(self):
+		return self._monitoring_active and self._send_queue_active
+
 	##~~ internal state management
 
 	def _changeState(self, newState):
@@ -1361,11 +1365,25 @@ class MachineCom(object):
 			self._serial.timeout = settings().getFloat(["serial", "timeout", "communication"])
 
 	def _continue_sending(self):
-		if self._state == self.STATE_PRINTING:
-			if not self._sendFromQueue() and not self.isSdPrinting():
-				self._sendNext()
-		elif self._state == self.STATE_OPERATIONAL or self._state == self.STATE_PAUSED:
-			self._sendFromQueue()
+		while self._active:
+
+			if self._state == self.STATE_OPERATIONAL or self._state == self.STATE_PAUSED or self.isSdPrinting():
+				# just send stuff from the command queue and be done with it
+				return self._sendFromQueue()
+
+			elif self._state == self.STATE_PRINTING:
+				# we are printing, we really want to send either something from the command
+				# queue or the next line from our file, so we only return here if we actually DO
+				# send something
+				if self._sendFromQueue():
+					# we found something in the queue to send
+					return True
+
+				elif self._sendNext():
+					# we sent the next line from the file
+					return True
+
+				self._logger.debug("No command sent on ok while printing, doing another iteration")
 
 	def _process_registered_message(self, line, feedback_matcher, feedback_controls, feedback_errors):
 		feedback_match = feedback_matcher.search(line)
@@ -1660,10 +1678,20 @@ class MachineCom(object):
 
 	def _sendNext(self):
 		with self._sendNextLock:
-			line = self._getNext()
-			if line is not None:
-				self._sendCommand(line)
+			while self._active:
+				# we loop until we've actually enqueued a line for sending
+				line = self._getNext()
+				if line is None:
+					# end of file, return false
+					return False
+
+				result = self._sendCommand(line)
 				self._callback.on_comm_progress()
+				if result:
+					# line sent, return true
+					return True
+
+				self._logger.debug("Command \"{}\" from file not enqueued, doing another iteration".format(line))
 
 	def _handleResendRequest(self, line):
 		try: