WRONG QUERY RESULTS

Analysis
========
When using index_merge for InnoDB tables with a primary key,
the server does not set read_set correctly for index scan after
optimization. This does not cause a problem in other cases
because InnoDB does create templates during first call to
index_read(). Innodb uses sql_stat_start to decide initializing
templates in index_read(). sql_stat_start is set to false at
handler creation and set to true during first call to index_read().
In case of sub-query, during optimization we scan the index
and reset it for index read for execution. Further call to
index_read() does uses the templates created at reset as
inited is set to true during optimize phase.

This leads to InnoDB not reading primary key of the rows and
furthur leads to mismatch during index merge.

Fix
====
Provide correct read_set for each index during index_reset
to innodb for creating the right column template for reading.