Only load an empty project if we don't have one already

We may have multiple projects if one of them is a temporary
project used for importing settings

Fixes https://gitlab.com/kicad/code/kicad/-/issues/5423

common/settings/settings_manager.cpp

@@ -741,6 +741,7 @@ bool SETTINGS_MANAGER::UnloadProject( PROJECT* aProject, bool aSave )
 
     // Immediately reload a null project; this is required until the rest of the application
     // is refactored to not assume that Prj() always works
+    if( m_projects.empty() )
         LoadProject( "" );
 
     // Remove the reference in the environment to the previous project