Revert changes 5fae763 (#169)

Change introduces significant amount of first-chance exceptions in certain mapping scenarios.

See #167 for details

src/Qwiq.Mapper/Attributes/AttributeMapperStrategy.cs

@@ -168,7 +168,7 @@ private static IEnumerable<PropertyInfo> PropertiesOnWorkItemCache(IPropertyInsp
  new { property, fieldName = PropertyInfoFieldCache(inspector, property)?.FieldName })
  .Where(
  t =>
- !string.IsNullOrEmpty(t.fieldName))
+ !string.IsNullOrEmpty(t.fieldName) && workItem.Fields.Contains(t.fieldName))
  .Select(t => t.property)
  .ToList();
  });