New: Improve path validation when handling paths from different OSes

(cherry picked from commit 0321368cc392d7a0a488409bf6bd586ba45497af)

Closes #2309

src/NzbDrone.Common.Test/EnsureTest/PathExtensionFixture.cs

@@ -1,4 +1,5 @@
-using NUnit.Framework;
+using NUnit.Framework;
+using NzbDrone.Common.Disk;
 using NzbDrone.Common.EnsureThat;
 using NzbDrone.Test.Common;
 
@@ -12,14 +13,14 @@ namespace NzbDrone.Common.Test.EnsureTest
         public void EnsureWindowsPath(string path)
         {
             WindowsOnly();
-            Ensure.That(path, () => path).IsValidPath();
+            Ensure.That(path, () => path).IsValidPath(PathValidationType.CurrentOs);
         }
 
         [TestCase(@"/var/user/file with, comma.mp3")]
         public void EnsureLinuxPath(string path)
         {
             PosixOnly();
-            Ensure.That(path, () => path).IsValidPath();
+            Ensure.That(path, () => path).IsValidPath(PathValidationType.CurrentOs);
         }
     }
 }

src/NzbDrone.Common.Test/PathExtensionFixture.cs

@@ -35,6 +35,7 @@ namespace NzbDrone.Common.Test
         [TestCase(@"\\Testserver\Test\file.ext", @"\\Testserver\Test\file.ext")]
         [TestCase(@"\\Testserver\Test\file.ext\\", @"\\Testserver\Test\file.ext")]
         [TestCase(@"\\Testserver\Test\file.ext   \\", @"\\Testserver\Test\file.ext")]
+        [TestCase(@"//CAPITAL//lower// ", @"\\CAPITAL\lower")]
         public void Clean_Path_Windows(string dirty, string clean)
         {
             WindowsOnly();