Fix copilot hint

Author: ufechner7

ext/VortexStepMethodControlPlotsExt.jl

@@ -174,8 +174,10 @@ function create_geometry_plot(body_aero::BodyAerodynamics, title, view_elevation
     set_plot_style(28; use_tex)
 
     panels = body_aero.panels
+    isempty(panels) && throw(ArgumentError("Cannot plot geometry: body_aero.panels is empty."))
+
     va = if body_aero.has_distributed_va
-        panels[1].va
+        body_aero._va
     else
         isa(body_aero.va, Tuple) ? body_aero.va[1] : body_aero.va
     end

test/plotting/test_plotting.jl

@@ -215,6 +215,15 @@ end
     end
 
     if backend == "ControlPlots"
+        body_aero_empty = create_body_aero()
+        empty!(body_aero_empty.panels)
+        @test_throws ArgumentError plot_geometry(
+            body_aero_empty,
+            "Rectangular_wing_geometry_empty_panels";
+            is_save=false,
+            is_show=false,
+        )
+
         body_aero_distributed = create_body_aero()
         n_panels = length(body_aero_distributed.panels)
         va_distribution = repeat([12.0 0.0 1.0], n_panels, 1)