message: fix uninitialized atlas packing context
diff: @@ -1617,8 +1617,7 @@ bool ImFontAtlasBuildWithStbTruetype(ImFontAtlas* atlas)
  // Start packing
  const int max_tex_height = 1024*32;
  - stbtt_pack_context spc;
  - memset(&spc, 0, sizeof(spc));
  + stbtt_pack_context spc = {};
  stbtt_PackBegin(&spc, NULL, atlas->TexWidth, max_tex_height, 0, atlas->TexGlyphPadding, NULL);
  stbtt_PackSetOversampling(&spc, 1, 1);
  