Change fallback order to use the first valid path which can be constructed

osu.Framework.Tests/Platform/UserStorageLookupTest.cs

···
         {
             try
             {
+                File.Delete(path1);
+                File.Delete(path2);
+            }
+            catch
+            {
+            }
+
+            try
+            {
                 Directory.Delete(path1, true);
                 Directory.Delete(path2, true);
             }
···
         }
 
         [Test]
-        public void TestSecondBaseExisting()
+        public void TestSecondBaseExistingStillPrefersFirst()
         {
             Directory.CreateDirectory(path2);
 
             using (var host = new StorageLookupHeadlessGameHost())
             {
                 runHost(host);
-                Assert.IsTrue(host.Storage.GetFullPath(string.Empty).StartsWith(path2, StringComparison.Ordinal));
+                Assert.IsTrue(host.Storage.GetFullPath(string.Empty).StartsWith(path1, StringComparison.Ordinal));
             }
         }
 
         [Test]
-        public void TestPrefersFirstBase()
+        public void TestSecondBaseUsedIfFirstFails()
         {
-            Directory.CreateDirectory(path1);
-            Directory.CreateDirectory(path2);
+            // write a file so directory creation fails.
+            File.WriteAllText(path1, "");
 
             using (var host = new StorageLookupHeadlessGameHost())
             {
                 runHost(host);
-                Assert.IsTrue(host.Storage.GetFullPath(string.Empty).StartsWith(path1, StringComparison.Ordinal));
+                Assert.IsTrue(host.Storage.GetFullPath(string.Empty).StartsWith(path2, StringComparison.Ordinal));
             }
         }
 

osu.Framework/Platform/GameHost.cs

···
                     return storage.GetStorageForDirectory(Name);
             }
 
-            // if an existing directory could not be found, use the first available valid path.
+            // if an existing directory could not be found, use the first path that can be created.
             foreach (var path in UserStoragePaths)
             {
-                var storage = GetStorage(path);
-
-                if (storage.ExistsDirectory(string.Empty))
-                    return storage.GetStorageForDirectory(Name);
+                try
+                {
+                    return GetStorage(path).GetStorageForDirectory(Name);
+                }
+                catch
+                {
+                    // may fail on directory creation.
+                }
             }
 
             throw new InvalidOperationException("No valid user storage path could be resolved.");