Avoid bad string conversion in RecordedBinder error log

BUG=271730529

Test: This was discovered by an existing fuzz test, and should be
reproducible that way. Or create a recording with record_binder and edit
the interface name to include an emoji or other multi-byte character.

Change-Id: I91b301f8930f5e3abbda531ce89e4b55a8c2e319