Fix unclear IsRepositoryExist logic (#24374)

There was only one `IsRepositoryExist` function, it did: `has && isDir`

However it's not right, and it would cause 500 error when creating a new
repository if the dir exists.

Then, it was changed to `has || isDir`, it is still incorrect, it
affects the "adopt repo" logic.

To make the logic clear:

* IsRepositoryModelOrDirExist
* IsRepositoryModelExist

routers/web/user/setting/adopt.go

@@ -31,7 +31,7 @@ func AdoptOrDeleteRepository(ctx *context.Context) {
 	root := user_model.UserPath(ctxUser.LowerName)
 
 	// check not a repo
-	has, err := repo_model.IsRepositoryExist(ctx, ctxUser, dir)
+	has, err := repo_model.IsRepositoryModelExist(ctx, ctxUser, dir)
 	if err != nil {
 		ctx.ServerError("IsRepositoryExist", err)
 		return