Closes https://github.com/MusicPlayerDaemon/MPD/issues/1644

This appears to have been fixed in some recent CURL version.

According to the latest WebDAV specification (RFC4918),
timestamp string in the getlastmodified property is formatted
as rfc1123-date, such as "Sun, 06 Nov 1994 08:49:37 GMT".
However, to process responses from servers in the older style
format specified in RFC2518, timestamps in the HTTP-date format
had better be accepted.

As described in the libcurl api documentation, curl_getdate() can handle
timestamp strings in HTTP-date formats, including rfc1123-date.

https://www.rfc-editor.org/rfc/rfc4918#section-15.7
https://www.rfc-editor.org/rfc/rfc2518.html#section-13.7
https://curl.se/libcurl/c/curl_getdate.html

Fixes compiler warning because formatting unscoped enums is deprecated
since libfmt 9.

This fixes #1616

This fixes a bug introduced in 87fa6bca where the FLAC encoder fails to
initialize unless libFLAC is built with Ogg support. When libFLAC is
built without Ogg support, FLAC__stream_encoder_set_ogg_serial_number
unconditionally returns false.

Don't require "log_file" setting, for "--no-config" operation.

Closes https://github.com/MusicPlayerDaemon/MPD/issues/1600

Calling data[fill] could trigger an assertion failure if
fill==data.size(), even if we call it only to take the address.

Instead of doing that, this commit changes the code to pointer
arithmetic.

Closes https://github.com/MusicPlayerDaemon/MPD/issues/1556

See also https://github.com/MusicPlayerDaemon/MPD/issues/1061

Closes https://github.com/MusicPlayerDaemon/MPD/issues/1570

This ensures that Partition::OnMixerVolumeChanged() invokes
MixerMemento::InvalidateHardwareVolume(), clearing the cached volume
level.

Closes https://github.com/MusicPlayerDaemon/MPD/issues/1526