MDEV-19055 Failures with temporary tables and Aria

There was two separate problems:
- Aria pagecache didn't properly handle re-reading of blocks
  that have given errors before (this triggered an assert)
- temporary tables that where opened several times where
  not properly closed in ALTER, REPAIR or OPTIMIZE table

Other things
- Added a couple of asserts that will make it easier to
  find problems like this in the future.

1 files changed, 2 insertions, 0 deletions

diff --git a/mysys/my_pread.c b/mysys/my_pread.c
index 08285738528..15586d00a6f 100644
--- a/mysys/my_pread.c
+++ b/mysys/my_pread.c
@@ -68,6 +68,8 @@ size_t my_pread(File Filedes, uchar *Buffer, size_t Count, my_off_t offset,
 
     if (readbytes != Count)
     {
+      /* We should never read with wrong file descriptor! */
+      DBUG_ASSERT(my_errno != 9);
       my_errno= errno;
       if (errno == 0 || (readbytes != (size_t) -1 &&
                          (MyFlags & (MY_NABP | MY_FNABP))))