This helps with ensuring that the generated CHM always has the inheritance diagrams as by default Doxygen creates it successfully even if dot is not found -- but without any graphs. Closes #15620. git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_3_0_BRANCH@75095 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775