Fix hang on stream termination if no frames can be captured

[cgutman]

Description

While testing with #707, I discovered an issue that was causing stream termination hangs that would prevent a client from reconnecting (or with #707, cause Sunshine to terminate itself). The issue is that the only time display_t::capture() will return to the capture thread or invoke the callback is when a frame is successfully captured or an error or reinit occurs. If it's just a normal timeout, the capture function will loop forever trying to capture a frame.

To fix this, I added a parameter to the snapshot_cb callback that indicates whether a frame was captured or if this is a callback invocation caused by a timeout. Now that snapshot_cb is being invoked for timeouts, it can check if capture should stop and return nullptr to indicate that.

Screenshot

Issues Fixed or Closed

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Dependency update (updates to dependencies)
• Documentation update (changes to documentation)
• Repository update (changes to repository files, e.g. .github/...)

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have added or updated the in code docstring/documentation-blocks for new or existing methods/components

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