Fonts: fixed a crash when trying to use AddFont() with MergeMode=true on a font that has already been rendered. (#9162)

docs/CHANGELOG.txt

@@ -74,6 +74,8 @@ Breaking Changes:
       until a shutdown of the owning context or font atlas.
     - The fact that handling of `FontDataOwnedByAtlas = false` was broken bypassed
       the issue altogether.
+  - Fixed a crash when trying to use AddFont() with MergeMode=true on a font that
+    has already been rendered. (#9162) [@ocornut, @cyfewlp]
   - Removed ImFontConfig::PixelSnapV added in 1.92 which turns out is unnecessary
     (and misdocumented). Post-rescale GlyphOffset is always rounded.
  - Popups: changed compile-time 'ImGuiPopupFlags popup_flags = 1' default value to be '= 0' for

imgui_draw.cpp

@@ -3049,6 +3049,7 @@ ImFont* ImFontAtlas::AddFont(const ImFontConfig* font_cfg_in)
     {
         IM_ASSERT(Fonts.Size > 0 && "Cannot use MergeMode for the first font"); // When using MergeMode make sure that a font has already been added before.
         font = font_cfg_in->DstFont ? font_cfg_in->DstFont : Fonts.back();
+        ImFontAtlasFontDiscardBakes(this, font, 0); // Need to discard bakes if the font was already used, because baked->FontLoaderDatas[] will change size. (#9162)
     }
 
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