Otherwise this code behaves incorrectly on getter-only properties: it
returns a meaningless field signature whereas the property has no field.
It's hard to come up with an example of when this could matter in
compiler code, but it's very noticeable in kotlinx-metadata-jvm
#KT-26188 Fixed
This should have no effect on the correct code currently because all
properties have at least a getter, but may help in debugging problems
with serialized metadata for properties
Alexander Udalov