[BUG] config-parser.c: line 89 - crash on comma in namespace mailbox

[Alek]

Hi!
On the latest versions (2.2.28, 2.2.29.x) we get crash on dovecot config parse.
Error in config parser when checking namespace mailbox name. 
Reason: comma in mailbox name.
Worked well in versions < 2.2.22. Do not know if it was working on 2.2.23-2.2.27, skipped this versions.

Example:
namespace inbox {
  mailbox "&BB4EQgQ,BEAEMAQyBDsENQQ9BD0ESwQ1-" {
    special_use = \Sent
  }
}

Error:
# dovecot -n
# 2.2.29.1 (e0b76e3): /etc/dovecot/dovecot.conf
# Pigeonhole version 0.4.18 (29cc74d)
doveconf: Panic: file config-parser.c: line 89 (config_add_type): assertion failed: (ret > 0)
doveconf: Error: Raw backtrace: /usr/lib64/dovecot/libdovecot.so.0(+0x9b89a) [0x7fa1f8cc789a] -> /usr/lib64/dovecot/libdovecot.so.0(default_fatal_handler+0x32) [0x7fa1f8cc81d2] -> /usr/lib64/dovecot/libdovecot.so.0(+0x2f81a) [0x7fa1f8c5b81a] -> /usr/bin/doveconf() [0x40b213] -> /usr/bin/doveconf(config_parser_apply_line+0x763) [0x40b983] -> /usr/bin/doveconf(config_parse_file+0x821) [0x40c351] -> /usr/bin/doveconf(main+0x255) [0x406845] -> /lib64/libc.so.6(__libc_start_main+0xfd) [0x7fa1f88b6d1d] -> /usr/bin/doveconf() [0x4051f9]
doveconf: Error: managesieve-login: dump-capability process killed with signal 6
doveconf: Panic: file config-parser.c: line 89 (config_add_type): assertion failed: (ret > 0)
doveconf: Error: Raw backtrace: /usr/lib64/dovecot/libdovecot.so.0(+0x9b89a) [0x7f6dfa20489a] -> /usr/lib64/dovecot/libdovecot.so.0(default_fatal_handler+0x32) [0x7f6dfa2051d2] -> /usr/lib64/dovecot/libdovecot.so.0(+0x2f81a) [0x7f6dfa19881a] -> /usr/bin/doveconf() [0x40b213] -> /usr/bin/doveconf(config_parser_apply_line+0x763) [0x40b983] -> /usr/bin/doveconf(config_parse_file+0x821) [0x40c351] -> /usr/bin/doveconf(main+0x255) [0x406845] -> /lib64/libc.so.6(__libc_start_main+0xfd) [0x7f6df9df3d1d] -> /usr/bin/doveconf() [0x4051f9]


Info:
&BB4EQgQ,BEAEMAQyBDsENQQ9BD0ESwQ1- - is a valid mailbox name for russian Outlook folder "Отправленные".