Fixed: UI loading when movie or root folder path is for wrong OS

(cherry picked from commit 5f7217844533907d7fc6287a48efb31987736c4c)

src/NzbDrone.Common/Extensions/PathExtensions.cs

@@ -170,6 +170,11 @@ namespace NzbDrone.Common.Extensions
 
         public static bool ContainsInvalidPathChars(this string text)
         {
+            if (text.IsNullOrWhiteSpace())
+            {
+                throw new ArgumentNullException("text");
+            }
+
             return text.IndexOfAny(Path.GetInvalidPathChars()) >= 0;
         }