When MAX_INDEXES is > 64, Key_map uses a special template implementation.
However, the fields keys_in_use_for_group_by and keys_in_use_for_order_by
were not initialized when used by a temporary table.
This was OK when using a Bitmap<64> template, but causes failure when
using the special template.

The solution is to explicitly initialize the two fields.

In addition, it was detected that argument key_to_save to is_set()
in TABLE::use_index() could be negative, this was corrected.
To prevent further problems like this, more asserts on valid arguments
were added in sql_bitmap.h.

No test case was added to this bugfix: A special configuration is
needed to trigger the problem, and several queries in the test suite
are vulnerable (all queries with materialized derived tables with
equality test on non-indexed columns). However, the problem is not
met in any standard test suite, since none of them use the option
MAX_INDEXES=128.