Avoid a NRE when alternate type info is not used.

Author: bclothier

Rubberduck.VBEEditor/ComManagement/TypeLibs/TypeInfoWrapper.cs

@@ -228,7 +228,7 @@ public void Dispose()
             (_container as IDisposable)?.Dispose();
 
             _typeInfoPointer.Dispose();
-            _typeInfoAlternatePointer.Dispose();
+            _typeInfoAlternatePointer?.Dispose();
         }
 
         TypeInfoVBEExtensions _vbeExtensions;