VS: Compute managed type from an existing configuration

It is not clear how multiple configurations should be handled here, but
using an existing configuration is at least better than the empty
configuration.

Source/cmVisualStudio10TargetGenerator.cxx

@@ -4134,7 +4134,8 @@ void cmVisualStudio10TargetGenerator::WriteProjectReferences(Elem& e0)
     }
 
     // Don't reference targets that don't produce any output.
-    if (dt->GetManagedType("") == cmGeneratorTarget::ManagedType::Undefined) {
+    if (dt->GetManagedType(this->Configurations[0]) ==
+        cmGeneratorTarget::ManagedType::Undefined) {
       e2.Element("ReferenceOutputAssembly", "false");
       e2.Element("CopyToOutputDirectory", "Never");
     }