Fix exception when stored media url is already absolute

(cherry picked from commit 49b3351c72)

src/Umbraco.Tests/Routing/MediaUrlProviderTests.cs

@@ -81,6 +81,19 @@ namespace Umbraco.Tests.Routing
             Assert.AreEqual(expected, resolvedUrl);
         }
 
+        [Test]
+        public void Get_Media_Url_Returns_Absolute_Url_If_Stored_Url_Is_Absolute()
+        {
+            const string expected = "http://localhost/media/rfeiw584/test.jpg";
+
+            var umbracoContext = GetUmbracoContext("http://localhost", mediaUrlProviders: new[] { _mediaUrlProvider });
+            var publishedContent = CreatePublishedContent(Constants.PropertyEditors.Aliases.UploadField, expected, null);
+
+            var resolvedUrl = umbracoContext.UrlProvider.GetMediaUrl(publishedContent, UrlMode.Relative);
+
+            Assert.AreEqual(expected, resolvedUrl);
+        }
+
         [Test]
         public void Get_Media_Url_Returns_Empty_String_When_PropertyType_Is_Not_Supported()
         {

src/Umbraco.Web/Routing/DefaultMediaUrlProvider.cs

@@ -45,6 +45,10 @@ namespace Umbraco.Web.Routing
             if (string.IsNullOrEmpty(path))
                 return null;
 
+            // the stored path is absolute so we just return it as is
+            if(Uri.IsWellFormedUriString(path, UriKind.Absolute))
+                return new Uri(path);
+
             Uri uri;
 
             if (current == null)