[enco] Not apply constant folding when instruction has output bag (#2897)

[enco] Not apply constant folding when instruction has output bag (#2897)

* [enco] Not apply constant folding when instruction has output bag

Until now, constant folding was even applied to the instructions which have output bag.
If then, constant folding tries to update network output buffer but it is not impossible.
Furthermore, the total result would be abnormal.
This commit will fix it by not applying constant folding when instruction has output bag and add related testcases.

Signed-off-by: Seok NamKoong <sk.namkoong@samsung.com>
* add TODO comment

* rename testcase