Fix read pipelining

Fix read pipelining

During read pipelining we must ensure that the buffer is sufficiently large
to read enough data to fill our pipelines. We also remove some code that
moved data to the start of the packet if we can. This was unnecessary
because of later code which would end up moving it anyway. The earlier move
was also incorrect in the case that |clearold| was 0. This would cause the
read pipelining code to fail with sufficiently large records.

Fixes #20197

Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Hugo Landau <hlandau@openssl.org>
Reviewed-by: Paul Dale <pauli@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/20208)