Don't register a new layer if not extruding a line

We do retracts/unretracts on different heights sometimes, for instance after a pause. This would get seen as a new layer. It's quite safe to say that purely retracts and unretracts on a different height do not constitute a layer in a normal g-code file. There would be nothing to draw anyway.

Contributes to issue CURA-8522. Fixes Ultimaker#10282.

plugins/GCodeReader/FlavorParser.py

@@ -198,7 +198,7 @@ def _gCode0(self, position: Position, params: PositionOptional, path: List[List[
 
             # Only when extruding we can determine the latest known "layer height" which is the difference in height between extrusions
             # Also, 1.5 is a heuristic for any priming or whatsoever, we skip those.
-            if z > self._previous_z and (z - self._previous_z < 1.5):
+            if z > self._previous_z and (z - self._previous_z < 1.5) and (params.x is not None or params.y is not None):
                 self._current_layer_thickness = z - self._previous_z # allow a tiny overlap
                 self._previous_z = z
         elif self._previous_extrusion_value > e[self._extruder_number]: