#17869: Fix medium trust issue

"Assembly.Location" propery is not allowed in medium trust.
Use the virtual path of the assembly file instead.

Work Item: 17869

--HG--
branch : 1.x

src/Orchard/Environment/Extensions/Loaders/ReferencedExtensionLoader.cs

@@ -53,11 +53,13 @@ namespace Orchard.Environment.Extensions.Loaders {
             if (assembly == null)
                 return null;
 
+            var assemblyPath = _virtualPathProvider.Combine("~/bin", descriptor.Id + ".dll");
+
             return new ExtensionProbeEntry {
                 Descriptor = descriptor,
-                LastWriteTimeUtc = File.GetLastWriteTimeUtc(assembly.Location),
+                LastWriteTimeUtc = _virtualPathProvider.GetFileLastWriteTimeUtc(assemblyPath),
                 Loader = this,
-                VirtualPath = _virtualPathProvider.Combine("~/bin", descriptor.Id + ".dll")
+                VirtualPath = assemblyPath
             };
         }