imgui_freetype: Assert if bitmap size exceed chunk size to avoid buff…

…er overflow. (ocornut#5731)

misc/freetype/imgui_freetype.cpp

@@ -508,7 +508,7 @@ bool ImFontAtlasBuildWithFreeTypeEx(FT_Library ft_library, ImFontAtlas* atlas, u
     // Allocate temporary rasterization data buffers.
     // We could not find a way to retrieve accurate glyph size without rendering them.
     // (e.g. slot->metrics->width not always matching bitmap->width, especially considering the Oblique transform)
-    // We allocate in chunks of 256 KB to not waste too much extra memory ahead. Hopefully users of FreeType won't find the temporary allocations.
+    // We allocate in chunks of 256 KB to not waste too much extra memory ahead. Hopefully users of FreeType won't mind the temporary allocations.
     const int BITMAP_BUFFERS_CHUNK_SIZE = 256 * 1024;
     int buf_bitmap_current_used_bytes = 0;
     ImVector<unsigned char*> buf_bitmap_buffers;
@@ -556,6 +556,7 @@ bool ImFontAtlasBuildWithFreeTypeEx(FT_Library ft_library, ImFontAtlas* atlas, u
                 buf_bitmap_current_used_bytes = 0;
                 buf_bitmap_buffers.push_back((unsigned char*)IM_ALLOC(BITMAP_BUFFERS_CHUNK_SIZE));
             }
+            IM_ASSERT(buf_bitmap_current_used_bytes + bitmap_size_in_bytes <= BITMAP_BUFFERS_CHUNK_SIZE); // We could probably allocate custom-sized buffer instead.
 
             // Blit rasterized pixels to our temporary buffer and keep a pointer to it.
             src_glyph.BitmapData = (unsigned int*)(buf_bitmap_buffers.back() + buf_bitmap_current_used_bytes);