Fix slow local image validation (#990)

* Check for local image directory existence to avoid tons of exceptions

MediaBrowser.LocalMetadata/Images/LocalImageProvider.cs

@@ -1,6 +1,7 @@
 using System;
 using System.Collections.Generic;
 using System.Globalization;
+using System.IO;
 using System.Linq;
 using MediaBrowser.Controller.Entities;
 using MediaBrowser.Controller.Entities.Audio;
@@ -65,6 +66,12 @@ namespace MediaBrowser.LocalMetadata.Images
 
             var path = item.ContainingFolderPath;
 
+            // Exit if the cache dir does not exist, alternative solution is to create it, but that's a lot of empty dirs...
+            if (!Directory.Exists(path))
+            {
+                return Array.Empty<FileSystemMetadata>();
+            }
+
             if (includeDirectories)
             {
                 return directoryService.GetFileSystemEntries(path)

MediaBrowser.Providers/Manager/MetadataService.cs

@@ -92,10 +92,7 @@ namespace MediaBrowser.Providers.Manager
             catch (Exception ex)
             {
                 localImagesFailed = true;
-                if (!(item is IItemByName))
-                {
-                    Logger.LogError(ex, "Error validating images for {0}", item.Path ?? item.Name ?? "Unknown name");
-                }
+                Logger.LogError(ex, "Error validating images for {0}", item.Path ?? item.Name ?? "Unknown name");
             }
 
             var metadataResult = new MetadataResult<TItemType>