Mesh: handle exceptions when running FreeCAD in headless mode

src/Mod/Mesh/Gui/AppMeshGui.cpp

@@ -27,6 +27,7 @@
 # include <Inventor/SoInput.h>
 # include <Inventor/nodes/SoSeparator.h>
 # include <Inventor/annex/ForeignFiles/SoSTLFileKit.h>
+# include <QApplication>
 #endif
 
 #include <Base/Interpreter.h>
@@ -147,7 +148,9 @@ PyMOD_INIT_FUNC(MeshGui)
 
     // instantiating the commands
     CreateMeshCommands();
-    (void)new MeshGui::CleanupHandler;
+    if (qApp) {
+        (void)new MeshGui::CleanupHandler;
+    }
     
     // try to instantiate flat-mesh commands
     try{

src/Mod/MeshPart/Gui/MeshFlatteningCommand.py

@@ -117,3 +117,6 @@ try:
 except ImportError:
     App.Console.PrintLog("flatmesh-commands are not available\n")
     App.Console.PrintLog("flatmesh needs pybind11 as build dependency\n")
+except AttributeError:
+    # Can happen when running FreeCAD in headless mode
+    pass