Optimize Font.FromName parser

For some fonts a valid registered name can include the font
settings (weight, size, etc.). The name parser should try to
validate the full name including provided settings first.

Xwt/Xwt.Drawing/Font.cs

@@ -131,13 +131,18 @@ namespace Xwt.Drawing
 			int i = name.LastIndexOf (' ');
 			int lasti = name.Length;
 			do {
+				if (lasti > 0 && IsFontSupported (name.Substring (0, lasti)))
+					break;
+				
 				string token = name.Substring (i + 1, lasti - i - 1);
 				FontStyle st;
 				FontWeight fw;
 				FontStretch fs;
 				double siz;
-				if (double.TryParse (token, NumberStyles.Any, CultureInfo.InvariantCulture, out siz)) // Try parsing the number first, since Enum.TryParse can also parse numbers
-					size = siz;
+				if (double.TryParse (token, NumberStyles.Any, CultureInfo.InvariantCulture, out siz)) { // Try parsing the number first, since Enum.TryParse can also parse numbers
+					if (size == -1) // take only first number
+						size = siz;
+				}
 				else if (Enum.TryParse<FontStyle> (token, true, out st) && st != FontStyle.Normal)
 					style = st;
 				else if (Enum.TryParse<FontWeight> (token, true, out fw) && fw != FontWeight.Normal)
@@ -167,6 +172,22 @@ namespace Xwt.Drawing
 				return Font.SystemFont;
 		}
 
+		static bool IsFontSupported (string fontNames)
+		{
+			LoadInstalledFonts ();
+
+			string[] names = fontNames.Split (new [] {','}, StringSplitOptions.RemoveEmptyEntries);
+			if (names.Length == 0)
+				throw new ArgumentException ("Font family name not provided");
+
+			foreach (var name in names) {
+				var n = name.Trim ();
+				if (installedFonts.ContainsKey (n))
+					return true;
+			}
+			return false;
+		}
+
 		static string GetSupportedFont (string fontNames)
 		{
 			LoadInstalledFonts ();
@@ -195,7 +216,8 @@ namespace Xwt.Drawing
 
 		static string GetDefaultFont (string unknownFont)
 		{
-			Console.WriteLine ("Font '" + unknownFont + "' not available in the system. Using '" + Font.SystemFont.Family + "' instead");
+			if (unknownFont != Font.SystemFont.Family) // ignore rare case when the default system font is not registered
+				Console.WriteLine ("Font '" + unknownFont + "' not available in the system. Using '" + Font.SystemFont.Family + "' instead");
 			return Font.SystemFont.Family;
 		}