WPIcal segfaults when cancelling loading field in visualize dialog

[auscompgeek]

Describe the bug

When I cancel loading a (calibrated or reference) field from the Visualize dialog, WPIcal segfaults.

#0  0x0000559ffef3584c in std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >::length (this=<optimized out>) at /usr/include/c++/11/bits/basic_string.h:927
#1  std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >::_M_assign (this=this@entry=0x55a001711940 <DisplayGui()::selected_field_map>, __str=<error reading variable: Cannot access memory at address 0x8>)
    at /usr/include/c++/11/bits/basic_string.tcc:259
#2  0x0000559ffef33f2c in std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >::assign (__str=..., this=0x55a001711940 <DisplayGui()::selected_field_map>) at /usr/include/c++/11/bits/basic_string.h:1356
#3  std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >::operator= (__str=..., this=0x55a001711940 <DisplayGui()::selected_field_map>) at /usr/include/c++/11/bits/basic_string.h:681
#4  DisplayGui () at /work/wpical/src/main/native/cpp/WPIcal.cpp:467
#5  0x0000559ffef5c4ef in std::function<void()>::operator() (this=<optimized out>) at /usr/include/c++/11/bits/std_function.h:586
#6  wpi::gui::CommonRenderFrame () at /work/wpigui/src/main/native/cpp/wpigui.cpp:459
#7  0x0000559ffef6031b in wpi::gui::PlatformRenderFrame () at /work/wpigui/src/main/native/opengl3/wpigui_opengl3.cpp:86
#8  0x0000559ffef5d925 in wpi::gui::Main () at /work/wpigui/src/main/native/cpp/wpigui.cpp:400
#9  0x0000559ffeec5fa5 in main (argc=<optimized out>, argv=<optimized out>) at /work/wpical/src/main/native/cpp/WPIcal.cpp:570

To Reproduce

1. Press Visualize
2. Press Load * Field (either button)
3. Cancel

Expected behavior

Cancelling the file open dialog should work, and not crash.

Desktop:

• OS: Fedora Linux 41
• WPILib version: 2025.1.1