Changed gcode regex slightly to be on the safe side (we don't want to accidentally capture comments etc)

octoprint/util/comm.py

@@ -801,7 +801,7 @@ class MachineCom(object):
 				return
 
 			if not self.isStreaming():
-				gcode = re.search('([GM][0-9]+)', cmd)
+				gcode = re.search("^\s*([GM]\d+)", cmd)
 				if gcode:
 					gcode = gcode.group(1)
 
@@ -812,7 +812,7 @@ class MachineCom(object):
 					if hasattr(self, gcodeHandler):
 						cmd = getattr(self, gcodeHandler)(cmd)
 
-			if cmd:
+			if cmd is not None:
 				self._doSend(cmd, sendChecksum)
 
 	def _doSend(self, cmd, sendChecksum=False):