obs-qsv11: Initialize allocator response

[kkartaltepe]

Description

Do more initialization.

Motivation and Context

We check that mids is a nullptr which may not be the case if this remains uninitialized. Earlier attempt to fix this assumed we faulted on the response itself being null but this wasnt the case.

fixes #11221

How Has This Been Tested?

Consulted the wisdom of the ancients (godbolt).

Types of changes

• Bug fix (non-breaking change which fixes an issue)

Checklist:

• [x] My code has been run through clang-format.
• [x] I have read the contributing document.
• [x] My code is not on the master branch.
• [x] The code has been tested.
• [x] All commit messages are properly formatted and commits squashed where appropriate.
• [x] I have included updates to all appropriate documentation.