Summary:
We've seen some crashes from toRSocketPayload, but aren't sure of the cause.
When we fail the DCHECK, there won't be any log output, so log before it if it's going to fail.
Reviewed By: passy
Differential Revision: D14131409
fbshipit-source-id: b71e043f0b5feac3d2e44a34cc38c72086f966ad