added path validation to add series/ recent folders.

NzbDrone.Api/Validation/PathValidator.cs

@@ -0,0 +1,18 @@
+using FluentValidation.Validators;
+using NzbDrone.Common;
+
+namespace NzbDrone.Api.Validation
+{
+    public class PathValidator : PropertyValidator
+    {
+        public PathValidator()
+            : base("Invalid Path")
+        {
+        }
+
+        protected override bool IsValid(PropertyValidatorContext context)
+        {
+            return context.PropertyValue.ToString().IsPathValid();
+        }
+    }
+}