otr: add missing return on error path

Due to a missing return, corrupt TLV data would cause an infinite loop
that consumes memory, eventually crashing the process.

Thanks to Ivan Markin for pointing this out.

Change-Id: Iaaf7c5f7ce911d3e542b86f6b942b15e2ccbdf3b
Reviewed-on: https://go-review.googlesource.com/35247
Run-TryBot: Adam Langley <agl@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
1 file changed