Popups: Fix a crash when a new window is created after a modal on the same frame. (#4920)

docs/CHANGELOG.txt

@@ -103,6 +103,7 @@ Other Changes:
   handled by core automatically for all kind of inputs. (#4858, #2787, #1992, #3383, #2525, #1320)
 - Fixed a situation where CTRL+Tab or Modal can occasionally lead to the creation of ImDrawCmd with zero triangles,
   which would makes the draw operation of some backends assert (e.g. Metal with debugging). (#4857)
+- Popups: Fixed a regression crash when a new window is created after a modal on the same frame. (#4920) [@rokups]
 - Tables, ImDrawListSplitter: Fixed erroneously stripping trailing ImDrawList::AddCallback() when submitted in
   last column or last channel and when there are no other drawing operation. (#4843, #4844) [@hoffstadt]
 - Tables: Fixed positioning of Sort icon on right-most column with some settings (not resizable + no borders). (#4918).

imgui.cpp

@@ -5890,7 +5890,9 @@ static ImGuiWindow* ImGui::FindBlockingModal(ImGuiWindow* window)
     for (int i = g.OpenPopupStack.Size - 1; i >= 0; i--)
     {
         ImGuiWindow* popup_window = g.OpenPopupStack.Data[i].Window;
-        if (popup_window == NULL || !popup_window->WasActive || !(popup_window->Flags & ImGuiWindowFlags_Modal)) // Check WasActive, because this code may run before popup renders on current frame.
+        if (popup_window == NULL || !(popup_window->Flags & ImGuiWindowFlags_Modal))
+            continue;
+        if (!popup_window->Active && !popup_window->WasActive)      // Check WasActive, because this code may run before popup renders on current frame, also check Active to handle newly created windows.
             continue;
         if (IsWindowWithinBeginStackOf(window, popup_window))       // Window is rendered over last modal, no render order change needed.
             break;

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               "1.87 WIP"
-#define IMGUI_VERSION_NUM           18610
+#define IMGUI_VERSION_NUM           18611
 #define IMGUI_CHECKVERSION()        ImGui::DebugCheckVersionAndDataLayout(IMGUI_VERSION, sizeof(ImGuiIO), sizeof(ImGuiStyle), sizeof(ImVec2), sizeof(ImVec4), sizeof(ImDrawVert), sizeof(ImDrawIdx))
 #define IMGUI_HAS_TABLE