Fixed cleaning titles that use underscores instead of spaces

src/NzbDrone.Core/Parser/Parser.cs

@@ -100,7 +100,7 @@ namespace NzbDrone.Core.Parser
                     RegexOptions.IgnoreCase | RegexOptions.Compiled)
             };
 
-        private static readonly Regex NormalizeRegex = new Regex(@"(\b(a|an|the|and|or|of)\b)|\W|_",
+        private static readonly Regex NormalizeRegex = new Regex(@"((?:\b|_)(a|an|the|and|or|of)(?:\b|_))|\W|_",
                                                                  RegexOptions.IgnoreCase | RegexOptions.Compiled);
 
         private static readonly Regex SimpleTitleRegex = new Regex(@"480[i|p]|720[i|p]|1080[i|p]|[x|h|x\s|h\s]264|DD\W?5\W1|\<|\>|\?|\*|\:|\|",