Fix bug trying to read (.charAt s 1) on 1-char strings
Fix bug trying to read (.charAt s 1) on 1-char strings

- bug was in ReadCacheImpl, which was testing for non-zero-length
  strings and unnecessarily allowed 1-char strings through

alexanderkiel/transit-clj,cognitect/transit-clj,jdunruh/transit-clj,borovsky/transit-clj