Move folder errors to state

The "Invalid" config attribute is retained for errors discovered during
config loading (empty path, duplicate ID). This can only be set or
cleared at config loading time.

Errors discovered during runtime (I/O problems, etc) are now in the
folder state instead. Changes to these are sent as any other folder
state change.

internal/config/wrapper.go

@@ -215,29 +215,6 @@ func (w *Wrapper) SetGUI(gui GUIConfiguration) {
 	w.replaces <- w.cfg.Copy()
 }
 
-// Sets the folder error state. Emits ConfigSaved to cause a GUI refresh.
-func (w *Wrapper) SetFolderError(id string, err error) {
-	w.mut.Lock()
-	defer w.mut.Unlock()
-
-	w.folderMap = nil
-
-	for i := range w.cfg.Folders {
-		if w.cfg.Folders[i].ID == id {
-			errstr := ""
-			if err != nil {
-				errstr = err.Error()
-			}
-			if errstr != w.cfg.Folders[i].Invalid {
-				w.cfg.Folders[i].Invalid = errstr
-				events.Default.Log(events.ConfigSaved, w.cfg)
-				w.replaces <- w.cfg.Copy()
-			}
-			return
-		}
-	}
-}
-
 // Returns whether or not connection attempts from the given device should be
 // silently ignored.
 func (w *Wrapper) IgnoredDevice(id protocol.DeviceID) bool {