The cause for the bug was two-fold:
1. Incorrect detection of whether a table is the first one in a query plan -
  "used_table & 1" actually checks if used_table is table with number "1".
2. Missing logic to delay the evaluation of (expensive) constant conditions
  during the execution phase.

The fix adds/changes:
The patch:
- removes incorrect treatment of expensive predicates from make_cond_for_table,
  and lets the caller decide when to evaluate expensive predicates.
- saves expensive constant conditions in JOIN::exec_const_cond,
  which is evaluated once in the beginning of JOIN::exec.