Fix transforming a gpencil bezier vertex changing it's handle type

Selecting a gpencil bezier vertex and move it would change the handle
type when set to "Auto".

This happened because of a mismatch between transform flag use
and BKE_nurb_bezt_handle_test which would change the handle type
when only the vertex (knot) was selected.

Resolve by treating both handles as selected when the knot is selected.

source/blender/editors/transform/transform_convert_gpencil_legacy.cc

@@ -360,7 +360,7 @@ static void createTransGPencil_curves(bContext *C,
                 BKE_nurb_bezt_handle_test(bezt,
                                           SELECT,
                                           hide_handles ? NURB_HANDLE_TEST_KNOT_ONLY :
-                                                         NURB_HANDLE_TEST_EACH,
+                                                         NURB_HANDLE_TEST_KNOT_OR_EACH,
                                           use_around_origins_for_handles_test);
                 need_handle_recalc = true;
               }