Steps to reproduce:
1. Open the attached project
2. Click "Hello->Hello" under the menu
3. Repeat step 2

Result: crash in gtk_menu_get_type

#0 0x007f2d9f06fac0 in funlockfile
#1 0x007fff563ceae0 in gtk_menu_get_type
#2 0x007fff563ceb80 in gtk_menu_popup
#3 0x007fff563cec60 in gtk_menu_bar_set_child_pack_direction
#4 0x007fff563cec90 in gtk_menu_item_toggle_size_allocate
#5 0x007fff563cecc0 in gtk_menu_item_toggle_size_allocate
#6 0x007fff563cece0 in g_closure_invoke
<...>

Reproduced with: 2017.3.0f1, 2017.3.0p2

Note: unable to reproduce on 2017.2.0f3, script causes editor to enter an infinite loop and reach StackOverflow
Editor log is full of
UnityEditor.Menu:SetChecked(String, Boolean)
CrashTest:ValidateHello() (at Assets/CrashTest.cs:13)