Add missing 'perform_prime' member-variable.

This caused that variable to always be (re)set to false, even when no plugin was present, due to the 'identity' conversion taking place. (Maybe we should stop that in general, since that implies that we copy the data even when no plugin is present.) In any case, even if it wouldn't have caused this particular bug, it's an oversight that should be fixed anyway.

should fix CURA-11084

cura/plugins/v0/gcodepath.proto

@@ -29,14 +29,15 @@ message GCodePath {
  bool retract = 8;
  bool unretract_before_last_travel_move = 9;
  bool perform_z_hop = 10;
- bool skip_agressive_merge_hint = 11;
- bool done = 12;
- double fan_speed = 13;
- string mesh_name = 14;
- cura.plugins.v0.PrintFeature feature = 15;
- SpeedDerivatives speed_derivatives = 16;
- int64 line_width = 17;
- int64 layer_thickness = 18;
- double flow_ratio = 19;
- bool is_bridge_path = 20;
+ bool perform_prime = 11;
+ bool skip_agressive_merge_hint = 12;
+ bool done = 13;
+ double fan_speed = 14;
+ string mesh_name = 15;
+ cura.plugins.v0.PrintFeature feature = 16;
+ SpeedDerivatives speed_derivatives = 17;
+ int64 line_width = 18;
+ int64 layer_thickness = 19;
+ double flow_ratio = 20;
+ bool is_bridge_path = 21;
 }