swirc: update to 3.4.7.

## [3.4.7] - 2024-03-12 ##
- Added command `/dcc`
- Added event `BATCH` (IRCv3). The following types were added:
  - `chathistory`
  - `netjoin`
  - `netsplit`
  - `znc.in/playback`
- Added tab completion for:
  - `/mode`
- Added the following config options:
  - `batch` (bool)
  - `dcc` (bool)
  - `dcc_cipher_suite` (string)
  - `dcc_own_ip` (string)
  - `dcc_port` (int)
  - `dcc_upload_dir` (string)
  - `multi_prefix` (bool)
- Did code optimizations:
  - Measure string length once, found by
    [PVS-Studio](https://pvs-studio.com/en/pvs-studio/).
  - ...
- Enabled `iconv_conversion` by default.
- Fixed an off-by-one error in the IRC module. The previous program
  versions weren't really affected however.
- Fixed building on any setup where Ncurses is built with opaque
  types.
- Fixed new [Coverity](https://scan.coverity.com/) defects
- Fixed the precision of the error log size in KB.
- Improved C++ exception handling. Among other things, handle if 'new'
  throws.
- Renamed option `ircv3_server_time` to `server_time` and enabled it
  by default.

(wiz)