Handle LOCKFILE logistics for ro

We need to check if a lockfile is valid to determine if we should
override the lock. Valid() is true if the lockfile couldn't be created
b/c of permissions or if the lockfile could be created and acquired.

common/settings/settings_manager.cpp

@@ -894,7 +894,7 @@ bool SETTINGS_MANAGER::LoadProject( const wxString& aFullPath, bool aSetActive )
     bool readOnly = false;
     LOCKFILE lockFile( fullPath );
 
-    if( !lockFile )
+    if( !lockFile.Valid() )
     {
         wxLogTrace( traceSettings, wxT( "Project %s is locked; opening read-only" ), fullPath );
         readOnly = true;

pcbnew/files.cpp

@@ -607,7 +607,7 @@ bool PCB_EDIT_FRAME::OpenProjectFiles( const std::vector<wxString>& aFileSet, in
 
     std::unique_ptr<LOCKFILE> lock = std::make_unique<LOCKFILE>( fullFileName );
 
-    if( !lock->Locked() )
+    if( !lock->Valid() )
     {
         msg.Printf( _( "PCB '%s' is already open by '%s' at '%s'." ), wx_filename.GetFullName(),
                 lock->GetUsername(), lock->GetHostname() );