Fix appending to windows causing a child window to be inserted to g.WindowsFocusOrder which eventually causes a crash. (#5515, #3496, #4797)

Amend a528398

docs/CHANGELOG.txt

@@ -60,6 +60,7 @@ Other Changes:
   next row in such state where subsequent SameLine() would move back to previous row.
 - Tabs: Fixed a crash when closing multiple windows (possible with docking only) with an
   appended TabItemButton(). (#5515, #3291) [@rokups]
+- Window: Fixed a potential crash when appending to a child window. (#5515, #3496, #4797) [@rokups]
 - IO: Added ImGuiKey_MouseXXX aliases for mouse buttons/wheel so all operations done on ImGuiKey
   can apply to mouse data as well. (#4921)
 - Nav: Fixed moving/resizing window with gamepad or keyboard when running at very high framerate.

imgui.cpp

@@ -5474,7 +5474,6 @@ static ImGuiWindow* CreateNewWindow(const char* name, ImGuiWindowFlags flags)
         g.Windows.push_front(window); // Quite slow but rare and only once
     else
         g.Windows.push_back(window);
-    UpdateWindowInFocusOrderList(window, true, window->Flags);
 
     return window;
 }
@@ -6087,8 +6086,6 @@ bool ImGui::Begin(const char* name, bool* p_open, ImGuiWindowFlags flags)
     const bool window_just_created = (window == NULL);
     if (window_just_created)
         window = CreateNewWindow(name, flags);
-    else
-        UpdateWindowInFocusOrderList(window, window_just_created, flags);
 
     // Automatically disable manual moving/resizing when NoInputs is set
     if ((flags & ImGuiWindowFlags_NoInputs) == ImGuiWindowFlags_NoInputs)
@@ -6116,6 +6113,7 @@ bool ImGui::Begin(const char* name, bool* p_open, ImGuiWindowFlags flags)
     // Update Flags, LastFrameActive, BeginOrderXXX fields
     if (first_begin_of_the_frame)
     {
+        UpdateWindowInFocusOrderList(window, window_just_created, flags);
         window->Flags = (ImGuiWindowFlags)flags;
         window->LastFrameActive = current_frame;
         window->LastTimeActive = (float)g.Time;

imgui.h

@@ -65,7 +65,7 @@ Index of this file:
 // Version
 // (Integer encoded as XYYZZ for use in #if preprocessor conditionals. Work in progress versions typically starts at XYY99 then bounce up to XYY00, XYY01 etc. when release tagging happens)
 #define IMGUI_VERSION               "1.89 WIP"
-#define IMGUI_VERSION_NUM           18805
+#define IMGUI_VERSION_NUM           18806
 #define IMGUI_CHECKVERSION()        ImGui::DebugCheckVersionAndDataLayout(IMGUI_VERSION, sizeof(ImGuiIO), sizeof(ImGuiStyle), sizeof(ImVec2), sizeof(ImVec4), sizeof(ImDrawVert), sizeof(ImDrawIdx))
 #define IMGUI_HAS_TABLE