This bug could manifest itself in a very rare cases when the optimizer
chose an execution plan by which a joined table was accessed by a table
scan and the optimizer was checking whether ranges checked for each record
could improve this plan. In such cases the optimizer evaluates range
conditions over a table that depend on other tables. For such conditions
the constructed SEL_ARG trees are marked as MAYBE_KEY. If a SEL_ARG object
constructed for a sargable condition marked as RANGE_KEY had the same
first key part as a MAYBE_KEY SEL_ARG object and the key_and() function
was called for this pair of SEL_ARG objects then an invalid SEL_ARG
object could be constructed that ultimately could lead to a crash before
the execution phase.