fix single digits test

Author: mythz

src/ServiceStack.Text/DynamicNumber.cs

@@ -674,11 +674,12 @@ public static bool TryParse(string strValue, out object result)
             if (strValue.Length == 1)
             {
                 int singleDigit = strValue[0];
-                if (singleDigit >= 48 && singleDigit <= 57) // 0 - 9
+                if (singleDigit >= '0' && singleDigit <= '9')
                 {
                     result = singleDigit - 48; // 0 
                     return true;
                 }
+                return false;
             }
 
             var hasDecimal = strValue.IndexOf('.') >= 0;

tests/ServiceStack.Text.Tests/DynamicNumberTests.cs

@@ -208,6 +208,7 @@ public void Can_text_for_numbers()
         {
             object x = null;
             Assert.That(DynamicNumber.TryParse("(", out x), Is.False);
+            Assert.That(DynamicNumber.TryParse("-", out x), Is.False);
         }