When converting `Chain` blocks to `Cord`, if a copy has to be made to avoid pinning wasted memory, avoid splitting the data into 4083-byte fragments.
When converting `Chain` blocks to `Cord`, if a copy has to be made to avoid
pinning wasted memory, avoid splitting the data into 4083-byte fragments.

PiperOrigin-RevId: 345207637

google/riegeli,google/riegeli,google/riegeli,google/riegeli