Bug fix cross plattform system drawing

[timsdesigns]

AC:

• needs to fix the bug Bug (Food4Rhino) - Could not load file or assembly 'System.Drawing.Common #4
• needs to continue as expected otherwise

Side effect:

• should fix the empty Rhino Scene error:

  Error
  System.NullReferenceException: Object reference not set to an instance of an object.
     at Web_Exporter.GltfExport.<>c__DisplayClass5_0.<SolveInstance>b__1() in C:\Data\Repos\GH-Helper\Web_Exporter\GLTF-Export\GltfExport.cs:line 106
  

  • if there was no gltf material found in rhino..
• previously caught, now handled instead
  • Permanently adding the result, and
  • Adding Runtime msg: "Please assign GLTF materials in Rhino before running this component." or "No valid GLTF materials found in Rhino." respectively