When SASL is active, it was possible that we read and decoded
more data off the wire than we initially wanted. The loop
processing this data terminated after only one message to
avoid delaying the calling thread, but this could delay
event delivery. As long as there is decoded SASL data in
memory, we must process it, before returning to the poll()
event loop.

This is a counterpart to the same kind of issue solved in

  commit 68d2c348

in a different area of the code

* src/remote/remote_driver.c: Process all pending SASL data