MDEV-10259 mysqld crash with certain statement length and...

order with Galera and encrypt-tmp-files=1

Problem:- If trans_cache (IO_CACHE) uses encrypted tmp file
then on next DML server will crash.

Case:-
 Lets take a case , we have a table t1 , We try to do 2 inserts in t1
  1. A really long insert so that trans_cache has to use temp_file
  2. Just a small insert

Analysis:- Actually server crashes from inside of galera
library.
/lib64/libc.so.6(abort+0x175)[0x7fb5ba779dc5]
/usr/lib64/galera/libgalera_smm.so(_ZN6galera3FSMINS_9TrxHandle5State...
mysys/stacktrace.c:247(my_print_stacktrace)[0x7fb5a714940e]
sql/signal_handler.cc:160(handle_fatal_signal)[0x7fb5a715c1bd]
sql/wsrep_hton.cc:257(wsrep_rollback)[0x7fb5bcce923a]
sql/wsrep_hton.cc:268(wsrep_rollback)[0x7fb5bcce9368]
sql/handler.cc:1658(ha_rollback_trans(THD*, bool))[0x7fb5bcd4f41a]
sql/handler.cc:1483(ha_commit_trans(THD*, bool))[0x7fb5bcd4f804]

but actual issue is not in galera but in mariadb, because for 2nd
insert we should never call rollback. We are calling rollback because
log_and_order fails it fails because write_cache fails , It fails
because after reinit_io_cache(trans_cache) , my_b_bytes_in_cache says 0
so we look into tmp_file for data , which is obviously wrong since temp
was used for previous insert and it no longer exist.
wsrep_write_cache_inc() reads the IO_CACHE in a loop, filling it with
my_b_fill() until it returns "0 bytes read". Later
MYSQL_BIN_LOG::write_cache() does the same.  wsrep_write_cache_inc()
assumes that reading a zero bytes past EOF leaves the old data in the
cache

Solution:- There is two issue in my_b_encr_read
1st we should never equal read_end to info->buffer. I mean this
does not make sense read_end should always point to end of buffer.
2nd For most of the case(apart from async IO_CACHE) info->pos_in_file
should be equal to info->buffer position wrt to temp file , since
in this case we are not changing info->buffer it should remain
unchanged.

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