Prevent panics with missing storage (#13164)

* The `.Use` of storageHandler before setting up the template renderer
causes a panic if there is an error to log.
* The error passed to `ctx.Error` in that case may contain sensitive
information and should not be rendered to the end user. We should
instead log the error and render a simple error message.
* There is no handling of missing avatars and this needs a 404. Minio
errors need to be mapped to standard golang errors such as
os.ErrNotExist.
* There is no logging when storage is set up.

Related #13159

Signed-off-by: Andrew Thornton <art27@cantab.net>

modules/storage/local.go

@@ -11,6 +11,7 @@ import (
 	"os"
 	"path/filepath"
 
+	"code.gitea.io/gitea/modules/log"
 	"code.gitea.io/gitea/modules/util"
 )
 
@@ -40,6 +41,7 @@ func NewLocalStorage(ctx context.Context, cfg interface{}) (ObjectStorage, error
 	}
 	config := configInterface.(LocalStorageConfig)
 
+	log.Info("Creating new Local Storage at %s", config.Path)
 	if err := os.MkdirAll(config.Path, os.ModePerm); err != nil {
 		return nil, err
 	}