This fixes a std::terminate() crash in the CURL storage plugin when
PropfindOperation::OnHeaders() throws an exception after receiving a
non-207 status.

Closes https://github.com/MusicPlayerDaemon/MPD/issues/1559

Fixes Android build failure with NDK r25 beta4 because "vulkan_beta.h"
was not found.

Closes https://github.com/MusicPlayerDaemon/MPD/issues/1536

`playlist_plugin` blocks use `name` to identify the plugins.

This was an experiment, but I decided I don't need that.

The build has been failing for a week or two because the package lists
in the image are outdated.

strlen() and strcpy() are provided by the <string.h> and <cstring>
headers (as functions in global and std namespaces, respectively).

Compilers MAY provide an implementation for either of the functions
without including the extra header but the existence of a declaration
without the header is not assured.

Fixes regression from commit 85f9863e

This issue occurs when playing HLS streaming delivered
from a server that does not support partial requests.
The issue is reproduced as follows(using Ubuntu 20.04 PC):

1. Prepare HLS example content.

$ mkdir test
$ ffmpeg -i example.flac -vn -c:a aac -b:a 128000 -f hls -hls_list_size 0 test/output.m3u8
(ffmpeg 4.2.4 is used)

2. Prepare web server without partial requests support.
(Docker version 20.10.12 and NGINX official Docker image is used)

$ docker run --name tmp-nginx-container -d nginx
$ docker cp tmp-nginx-container:/etc/nginx/conf.d/default.conf .
$ docker rm -f tmp-nginx-container

Edit default.conf and add "max_ranges 0;" to "location / {...}".
This disables partial requests support,
removes 'Accept-Ranges: bytes' header from the server response.
Then, run the server:

$ docker run --name test-nginx -v $PWD/test:/usr/share/nginx/html:ro -v $PWD/default.conf:/etc/nginx/conf.d/default.conf -d -p 8080:80 nginx

3. Setup MPD to Play the next URL.

http://address-of-the-server:8080/output.m3u8

Seeking this stream results in "exception: Not seekable".

AVFMTCTX_UNSEEKABLE signals the stream is not seekable
according to FFmpeg source code description:
https://github.com/FFmpeg/FFmpeg/blob/8e98dfc57fd05c49095dd964456a7acbb6da634c/libavformat/avformat.h#L1181

Fixes part 4 of https://github.com/MusicPlayerDaemon/MPD/issues/1490

Fixes part 1 of https://github.com/MusicPlayerDaemon/MPD/issues/1490