Fixed sort urls with no params not building full path

The provided partial path would be return which may not resolve to the
full URL when used on systems like those hosting BookStack on a
sub-path.
Fixes #4201

app/helpers.php

@@ -147,7 +147,7 @@ function icon(string $name, array $attrs = []): string
 }
 
 /**
- * Generate a url with multiple parameters for sorting purposes.
+ * Generate a URL with multiple parameters for sorting purposes.
  * Works out the logic to set the correct sorting direction
  * Discards empty parameters and allows overriding.
  */
@@ -172,7 +172,7 @@ function sortUrl(string $path, array $data, array $overrideData = []): string
     }
 
     if (count($queryStringSections) === 0) {
-        return $path;
+        return url($path);
     }
 
     return url($path . '?' . implode('&', $queryStringSections));