linux-capture: Log error if adjusted size geometry is zero

[dfaure-kdab]

Description

If after adjustments (crop settings) the size is 0x0 or negative in one component, the error message was just "shm failed".

Motivation and Context

What happened was, I used obs a long time ago on a 4k screen,
and wanted to record only the topleft quarter, so I had
crop right: 1920px, crop bottom: 1080px.
On an HD screen, this left... nothing. The adjusted size was 0x0
and shmget(0) returns an error, so all I could see on stderr was
"xshm-input: failed to attach shm !"

This made me dig very much into xshm problems, when in fact
a simple message about the adjusted size being 0x0 would have
helped tremendously.

While at it, also catch the case of crop being bigger than the screen.

How Has This Been Tested?

Tested on Linux with a Screen Capture source where the crop is equal or bigger than the screen dimension.

Types of changes

• Tweak (improved error handling)

Checklist:

• My code has been run through clang-format.
• I have read the contributing document.
• My code is not on the master branch.
  Not sure what this means. It's a MR for the master branch, shouldn't it be?
• The code has been tested.
• All commit messages are properly formatted and commits squashed where appropriate.
• I have included updates to all appropriate documentation.

[Lain-B]

Not sure what this means. It's a MR for the master branch, shouldn't it be?

We mean master branch of your fork. Just keeps things tidy and prevents situations where the submitter might need to sync and rebase.

[norihiro]

The commit title should start from a verb and it should be capitalized.
Maybe, "Log error if adjusted size geometry is zero" would be better.

[Lain-B]

I suppose this is fine. Anyone else have an opinion on the wording?