[skip ci] [FEM] don't hide Gmsh mesh by default
[skip ci] [FEM] don't hide Gmsh mesh by default

it is very annoying that the mesh is hided when closing the task dialog because one often has to play with the Gmsh properties and need to see the mesh.
See also https://forum.freecadweb.org/viewtopic.php?f=18&t=56401&start=10#p489734

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