Fixed retractionZHop setting for Z timelapses

Solves issue reported in #1148 for 1.3.0rc1

src/octoprint/server/api/timelapse.py

@@ -204,15 +204,15 @@ def setTimelapseConfig():
 				else:
 					return make_response("Invalid value for interval: %d" % interval)
 
-		if "retractionZHop" in request.values:
+		if "retractionZHop" in data:
 			config["options"] = {
 				"retractionZHop": 0
 			}
 
 			try:
-				retractionZHop = float(request.values["retractionZHop"])
+				retractionZHop = float(data["retractionZHop"])
 			except ValueError:
-				return make_response("Invalid value for retraction Z-Hop: %r" % request.values["retractionZHop"])
+				return make_response("Invalid value for retraction Z-Hop: %r" % data["retractionZHop"])
 			else:
 				if retractionZHop > 0:
 					config["options"]["retractionZHop"] = retractionZHop

src/octoprint/timelapse.py

@@ -617,7 +617,7 @@ def process_post_roll(self):
 		Timelapse.process_post_roll(self)
 
 	def _on_z_change(self, event, payload):
-		if self._retraction_zhop != 0:
+		if self._retraction_zhop != 0 and payload["old"] is not None and payload["new"] is not None:
 			# check if height difference equals z-hop or is negative, if so don't take a picture
 			diff = round(payload["new"] - payload["old"], 3)
 			zhop = round(self._retraction_zhop, 3)