Tweak Enum.TryParse whitespace skipping slightly

src/mscorlib/src/System/Enum.cs

@@ -428,7 +428,7 @@ private static bool TryParseEnum(Type enumType, String value, bool ignoreCase, r
                 StringComparison.OrdinalIgnoreCase : 
                 StringComparison.Ordinal;
 
-            int valueIndex = 0;
+            int valueIndex = firstNonWhitespaceIndex;
             while (valueIndex <= value.Length) // '=' is to handle invalid case of an ending comma
             {
                 // Find the next separator, if there is one, otherwise the end of the string.