FileServer crash - readd user

[KingKili]

When adding a client after he got removed because of timeout, the Server crashes with following back-trace.
munmap_chunk(): invalid pointer

Thread 3 "csync" received signal SIGABRT, Aborted.
[Switching to Thread 0x7ffff66b9700 (LWP 924)]
__GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:50
50	  return ret;
(gdb) ba
#0  __GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:50
#1  0x00007ffff6edc561 in __GI_abort () at abort.c:79
#2  0x00007ffff6f34927 in __libc_message (action=action@entry=do_abort, fmt=fmt@entry=0x7ffff703e579 "%s\n")
    at ../sysdeps/posix/libc_fatal.c:181
#3  0x00007ffff6f3ae0c in malloc_printerr (str=str@entry=0x7ffff703fe60 "munmap_chunk(): invalid pointer") at malloc.c:5350
#4  0x00007ffff6f3b364 in munmap_chunk (p=<optimized out>) at malloc.c:2846
#5  0x000000000040ee18 in __gnu_cxx::new_allocator<char>::deallocate (this=0x7ffff66b88d0, 
    __p=0x7fffe8000fe0 "sync/user0/.csync.folders") at /usr/include/c++/8/ext/new_allocator.h:125
#6  0x000000000040e2b1 in std::allocator_traits<std::allocator<char> >::deallocate (__a=..., 
    __p=0x7fffe8000fe0 "sync/user0/.csync.folders", __n=31) at /usr/include/c++/8/bits/alloc_traits.h:462
#7  0x000000000040d5e8 in std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >::_M_destroy (
    this=0x7ffff66b88d0, __size=30) at /usr/include/c++/8/bits/basic_string.h:226
#8  0x000000000040cd88 in std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >::_M_dispose (
    this=0x7ffff66b88d0) at /usr/include/c++/8/bits/basic_string.h:221
#9  0x000000000040bef6 in std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >::~basic_string (
    this=0x7ffff66b88d0, __in_chrg=<optimized out>) at /usr/include/c++/8/bits/basic_string.h:647
#10 0x000000000042fde5 in FilesystemServer::FilesystemServer (this=0x7fffe8002630, path="", clientsToDo=0x7fffe80025e8)
    at src/Filesystem.cpp:341
#11 0x00000000004290ec in FileServerUser::FileServerUser (this=0x7fffe8002560, username="", password="") at src/FileServerUser.cpp:9
#12 0x00000000004229ac in FileServer2::addUser (this=0x7fffffffd320, u=0x6c3168) at src/FileServer2.cpp:203
#13 0x0000000000422d42 in FileServer2::onClientHelloMessage (this=0x7fffffffd320, msg=0x7ffff66b8d30) at src/FileServer2.cpp:255
#14 0x00000000004224e3 in FileServer2::consumerTask (this=0x7fffffffd320) at src/FileServer2.cpp:158
#15 0x0000000000423ac3 in std::__invoke_impl<void, void (FileServer2::*)(), FileServer2*> (
    __f=@0x6c4190: (void (FileServer2::*)(FileServer2 * const)) 0x42240c <FileServer2::consumerTask()>, __t=@0x6c4188: 0x7fffffffd320)
    at /usr/include/c++/8/bits/invoke.h:73
#16 0x0000000000423663 in std::__invoke<void (FileServer2::*)(), FileServer2*> (
    __fn=@0x6c4190: (void (FileServer2::*)(FileServer2 * const)) 0x42240c <FileServer2::consumerTask()>, 
    __args#0=@0x6c4188: 0x7fffffffd320) at /usr/include/c++/8/bits/invoke.h:95
#17 0x00000000004251f7 in std::thread::_Invoker<std::tuple<void (FileServer2::*)(), FileServer2*> >::_M_invoke<0ul, 1ul> (
    this=0x6c4188) at /usr/include/c++/8/thread:234
#18 0x00000000004251b2 in std::thread::_Invoker<std::tuple<void (FileServer2::*)(), FileServer2*> >::operator() (this=0x6c4188)
    at /usr/include/c++/8/thread:243
#19 0x0000000000425196 in std::thread::_State_impl<std::thread::_Invoker<std::tuple<void (FileServer2::*)(), FileServer2*> > >::_M_run
    (this=0x6c4180) at /usr/include/c++/8/thread:186
#20 0x00007ffff7b04513 in execute_native_thread_routine () at ../../../../../libstdc++-v3/src/c++11/thread.cc:80
#21 0x00007ffff7281594 in start_thread (arg=<optimized out>) at pthread_create.c:463
#22 0x00007ffff6fb500f in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:95
(gdb)