Fonts, Context: assert that ImFontAtlas has no other references when destroying an owned atlas. (#9426)

docs/CHANGELOG.txt

@@ -95,6 +95,7 @@ Other Changes:
     calling ClearFonts() during rendering.
   - Fixed an issue where passing a manually created ImFontAtlas to CreateContext() would
     incorrectly destroy it in DestroyContext() when ref-count gets back to zero. (#9426)
+  - Destroying an ImGui context using a ImFontAtlas checks that the later has no references.
 - Nav:
   - Fixed context menu activation with gamepad erroneously testing for _NavEnableKeyboard
     instead of _NavEnableGamepad. (#9454, #8803, #9270) [@Clownacy]

imgui.cpp

@@ -4495,10 +4495,14 @@ void ImGui::Shutdown()
     for (ImFontAtlas* atlas : g.FontAtlases)
     {
         UnregisterFontAtlas(atlas);
-        if (atlas->RefCount == 0 && atlas->OwnerContext == &g)
+        if (atlas->OwnerContext == &g)
         {
-            atlas->Locked = false;
-            IM_DELETE(atlas);
+            IM_ASSERT(atlas->RefCount == 0 && "Destroying context owning a ImFontAtlas which is still used elsewhere!");
+            if (atlas->RefCount == 0)
+            {
+                atlas->Locked = false;
+                IM_DELETE(atlas);
+            }
         }
     }
     g.DrawListSharedData.TempBuffer.clear();