INSERT ... SELECT ...

Problem was that when bulk insert is used on an empty
table/partition, it disables the indexes for better
performance, but in this specific case it also tries
to read from that partition using an index, which is
not possible since it has been disabled.

Solution was to allow index reads on disabled indexes
if there are no records.

Also reverted the patch for bug#38005, since that was a workaround
in the partitioning engine instead of a fix in myisam.

mysql-test/r/partition.result:
  Bug#46639: 1030 (HY000): Got error 124 from storage engine on
  INSERT ... SELECT ...
  
  updated result file
mysql-test/t/partition.test:
  Bug#46639: 1030 (HY000): Got error 124 from storage engine on
  INSERT ... SELECT ...
  
  Added testcase
sql/ha_partition.cc:
  Bug#46639: 1030 (HY000): Got error 124 from storage engine on
  INSERT ... SELECT ...
  
  reverted the patch for bug#38005, since that was a workaround
  around this problem, not needed after fixing it in myisam.
storage/myisam/mi_search.c:
  Bug#46639: 1030 (HY000): Got error 124 from storage engine on
  INSERT ... SELECT ...
  
  Return HA_ERR_END_OF_FILE instead of HA_ERR_WRONG_INDEX
  when there are no rows.