Transfer issues with files with long Unicode filenames

[tsudoko]

Filename: ～～～～～～～～～～～～～～～～～～～～～～～～～～～～～～～～～～～～
Sending from Linux: uTox stops redrawing, but the transfer does work
Sending from Windows:

• the filename is wrong:
  
• trying to save that file on Linux made uTox crash:

Program received signal SIGSEGV, Segmentation fault.
[Switching to Thread 0x7fffd77bd700 (LWP 30942)]
0x00007ffff4bc64ea in strlen () from /lib64/libc.so.6
(gdb) bt
#0  0x00007ffff4bc64ea in strlen () from /lib64/libc.so.6
#1  0x00007ffff306fa9a in ?? () from /usr/lib64/libgtk-x11-2.0.so.0
#2  0x00007ffff305479b in ?? () from /usr/lib64/libgtk-x11-2.0.so.0
#3  0x00007ffff318e77f in ?? () from /usr/lib64/libgtk-x11-2.0.so.0
#4  0x00007ffff3193843 in ?? () from /usr/lib64/libgtk-x11-2.0.so.0
#5  0x00007ffff3193bd9 in ?? () from /usr/lib64/libgtk-x11-2.0.so.0
#6  0x00007ffff318ce48 in ?? () from /usr/lib64/libgtk-x11-2.0.so.0
#7  0x00007ffff318e0ce in gtk_tree_model_foreach () from /usr/lib64/libgtk-x11-2.0.so.0
#8  0x00007ffff30558d4 in gtk_entry_completion_complete () from /usr/lib64/libgtk-x11-2.0.so.0
#9  0x00007ffff304e9e0 in ?? () from /usr/lib64/libgtk-x11-2.0.so.0
#10 0x00007ffff2cf8527 in ?? () from /usr/lib64/libgdk-x11-2.0.so.0
#11 0x00007ffff061e343 in ?? () from /usr/lib64/libglib-2.0.so.0
#12 0x00007ffff061d925 in g_main_context_dispatch () from /usr/lib64/libglib-2.0.so.0
#13 0x00007ffff061dc88 in ?? () from /usr/lib64/libglib-2.0.so.0
#14 0x00007ffff061df4a in g_main_loop_run () from /usr/lib64/libglib-2.0.so.0
#15 0x00007ffff3043ca2 in gtk_dialog_run () from /usr/lib64/libgtk-x11-2.0.so.0
#16 0x0000000000413418 in gtk_savethread (args=0x7fffe801c7a0) at xlib/gtk.c:127
#17 0x00007ffff63893a4 in start_thread () from /lib64/libpthread.so.0
#18 0x00007ffff4c2c8ed in clone () from /lib64/libc.so.6