cmd/syncthing, lib/model: Handle rel/abs paths for config/protected paths (fixes #3183)

GitHub-Pull-Request: https://github.com/syncthing/syncthing/pull/3995

lib/model/model.go

@@ -285,7 +285,8 @@ func (m *Model) warnAboutOverwritingProtectedFiles(folder string) {
 		}
 
 		// check if file is ignored
-		if ignores.Match(protectedFilePath).IsIgnored() {
+		relPath, _ := filepath.Rel(folderLocation, protectedFilePath)
+		if ignores.Match(relPath).IsIgnored() {
 			continue
 		}