Fixed Parser.Parser.Normalize returns empty string (#991)

Parser.Parser.Normalize returns empty string when name doesn't have any
alphanumeric characters. It messes up Series at least.
To prevent this issue, if normalized string is empty, it just returns
received name variable. In this case user has to carefully set file names but
it is better than messed up Series.

API.Tests/Parser/ParserTest.cs

@@ -139,6 +139,7 @@ namespace API.Tests.Parser
         [InlineData("Darker Than_Black", "darkerthanblack")]
         [InlineData("Citrus", "citrus")]
         [InlineData("Citrus+", "citrus+")]
+        [InlineData("카비타", "카비타")]
         [InlineData("", "")]
         public void NormalizeTest(string input, string expected)
         {