fix(iv): Bug fix for iv window loosing focus on mac on startup

[soswow]

Description

Master version of the iv today when opening on mac sometimes opens without a focus, which causes top menu bar not to be populated (just iv on the left). Workaround is to switch back and forth once to and from another app for menu bar too get populated.

It is unclear to me how reliably replicate the bug so that I have a solid prove, that this fix works. But since building with this line it never happend to me yet.

Maybe more knowledgable in Qt can verify if it makes sense.

Checklist:

• I have read the contribution guidelines.
• I have updated the documentation, if applicable. (Check if there is no
  need to update the documentation, for example if this is a bug fix that
  doesn't change the API.)
• I have ensured that the change is tested somewhere in the testsuite
  (adding new test cases if necessary).
• If I added or modified a C++ API call, I have also amended the
  corresponding Python bindings (and if altering ImageBufAlgo functions, also
  exposed the new functionality as oiiotool options).
• My code follows the prevailing code style of this project. If I haven't
  already run clang-format before submitting, I definitely will look at the CI
  test that runs clang-format and fix anything that it highlights as being
  nonconforming.

[lgritz]

Thanks. I encounter this bug, too, but had no idea how to fix. I will test on my end.

[lgritz]

LGTM

I don't understand how or why this works, but I can totally confirm that it fixes the problem for me. I'd been encountering this for a while, but assumed it was some interaction between my still being on an old version of MacOS, and whatever version of Qt I had, or some other combination specific to me. I never would have known how to fix it entirely on our end with just one more Qt call. Thanks for fixing!!