Only do the processing if there's data to process in GCoder

printrun/gcoder.py

@@ -134,6 +134,7 @@ class GCode(object):
         self.lines = [Line(l2) for l2 in
                       (l.strip() for l in data)
                       if l2]
+        if self.lines:
             self._preprocess_lines()
             self.filament_length = self._preprocess_extrusion()
             self._create_layers()