Use a fall back font when files contain characters that do not exist in the chosen font.

[jonashertzman]

Maybe something like this could be used to find a suitable font:

	private static string FindFont(int codePoint)
	{
		foreach (FontFamily family in Fonts.SystemFontFamilies)
		{
			var typefaces = family.GetTypefaces();
			foreach (Typeface typeface in typefaces)
			{
				typeface.TryGetGlyphTypeface(out GlyphTypeface glyph);
				if (glyph != null && glyph.CharacterToGlyphMap.TryGetValue(codePoint, out _))
				{
					if (family.FamilyNames.TryGetValue(XmlLanguage.GetLanguage("en-us"), out string familyName))
					{
						return familyName;
					}
				}
			}
		}
		return "";
	}