Ensure that if we don't have any values we don't crash

I'm a bit suspicious that re-enabling that exception might be unsafe,
so let's be a bit friendlier.

Author: jasonmalinowski

src/VisualStudio/Core/Impl/ProjectSystem/CPS/CPSProjectFactory.cs

@@ -151,11 +151,15 @@ public async Task<IWorkspaceProjectContext> CreateProjectContextAsync(Guid id, s
         const string itemName = BuildPropertyNames.IntermediateAssembly;
 
         var values = data.GetItemValues(itemName);
-        if (values.Length != 1)
+        if (values.Length > 1)
         {
             var joinedValues = string.Join(";", values);
             throw new InvalidProjectDataException(itemName, joinedValues, $"Item group '{itemName}' is required to specify a single value: '{joinedValues}'.");
         }
+        else if (values.Length == 0)
+        {
+            return null;
+        }
 
         var path = values[0];