ffmpeg_patches: add amfenc delay/buffering fix

[psyke83]

Description

This resolves the issue in which the last captured frame is delayed by 1ms, which
is especially noticeable in low framerate content (such as desktop streaming)
on the amfenc encoder.

Issues Fixed or Closed

Fixes all reports related to delay with callback capture using the amfenc encoder:

• AMD AMF: Last frames not showing up when screen updates are ending [Windows] Sunshine#122
• Low FPS/High delay on desktop Sunshine#387
• Capturing images by callback, rather than pulling Causes Desktop issues. Sunshine#412

N.B. nvenc also experiences delay that is reported in some of the above issues. For those cases, it is resolved via a separate PR: LizardByte/Sunshine#507

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)
• Documentation update (changes to documentation)
• Repository update (changes to repository files)

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

[psyke83]

(added a test commit to see if cleaning the working tree before patching helps resolve the issue)

[ReenigneArcher]

@zycboss this is not a support channel...