Add underscore to host part of URI regex (#2633)

Fixes #2632

src/NzbDrone.Common/Http/HttpUri.cs

@@ -8,7 +8,7 @@ namespace NzbDrone.Common.Http
 {
     public class HttpUri : IEquatable<HttpUri>
     {
-        private static readonly Regex RegexUri = new Regex(@"^(?:(?<scheme>[a-z]+):)?(?://(?<host>[-A-Z0-9.]+)(?::(?<port>[0-9]{1,5}))?)?(?<path>(?:(?:(?<=^)|/)[^/?#\r\n]+)+/?|/)?(?:\?(?<query>[^#\r\n]*))?(?:\#(?<fragment>.*))?$", RegexOptions.Compiled | RegexOptions.IgnoreCase);
+        private static readonly Regex RegexUri = new Regex(@"^(?:(?<scheme>[a-z]+):)?(?://(?<host>[-_A-Z0-9.]+)(?::(?<port>[0-9]{1,5}))?)?(?<path>(?:(?:(?<=^)|/)[^/?#\r\n]+)+/?|/)?(?:\?(?<query>[^#\r\n]*))?(?:\#(?<fragment>.*))?$", RegexOptions.Compiled | RegexOptions.IgnoreCase);
 
         private readonly string _uri;
         public string FullUri => _uri;