Resolve using env/project if lib isn't found

Relative include commands resolve in the following order:

1. local to the file from which they are included
2. local to the project
3. local to the SPICE_LIB_DIR directory

Fixes https://gitlab.com/kicad/code/kicad/issues/13083

eeschema/sim/sim_lib_mgr.cpp

@@ -115,6 +115,11 @@ SIM_LIBRARY& SIM_LIB_MGR::SetLibrary( const wxString& aLibraryPath, REPORTER* aR
 
         try
         {
+            wxFileName fn( fullPath );
+
+            if( !fn.Exists() )
+                fullPath = aLibPath;
+
             fullPath = ResolveLibraryPath( fullPath, m_project );
         }
         catch( ... )