Use non-blocking std::atomic_flag instead of std::atomic_bool, because the flag
does not require linking against libatomic on RISC-V 64bit.

Closes: #1018725

Move check of layer self-nesting to parsing stage from rendering.

Closes: #1019499

Gbp-Dch: Ignore

I wrongly thought the option is for extracting names of commit authors to
changelog subtitles. But gbp(1) already does it automatically.

Gbp-Dch: ignore

Ignore very-long-line-length-in-source-file in JSON examples.

Gbp-Dch: ignore

New patches:
 * Init-keyframe.patch
 * Check-empty-frames.patch
 * No-cyclic-structures.patch
 * Positive-points.patch
 * Stop-VBezier-length-overflow.patch
Amended patches:
 * Check-buffer-length.patch
 * Fortify-FreeType-raster.patch

Closes: #994614

Closes: #974095

Closes: #984323

Closes: #988885

 * Also add Freetype-raster.patch for fix CVE-2021-31321.
 * Add Fortify-lottie-parser.patch for fix crashes on invalid input.

Closes: #988885

Fixes lintian: upstream-metadata-file-is-missing
See https://lintian.debian.org/tags/upstream-metadata-file-is-missing.html for more details.

Update to upstream version '0.1+dfsg'
with Debian dir aff6754a9423910f38cb1e6f09b3d01932037734

Although, there is a binary incompatibility in the LOTNode structure, I
do not increase soversion because none client in Debian archive reads
the modified structure, and so migration is not necessary.

 - Permit cache support.

Update to upstream version '0~git20200305.a717479+dfsg'
with Debian dir 2ef1105d9fa8cf51b4bd26cf971d794ff3b6b2d0