NewRouter for servers section throw exception if no path is specified

[NaerChang2]

Following servers section is causing exception because URL.EscapedPath() returns empty and index access is missing length check.

servers:
  - url: https://example.com

So it's causing line 46 to throw out of index exception.

if path[len(path)-1] == '/' {
	...
}

For better user experience a simple len(path) check will be nice.

[NaerChang2]

PR: #408