WinGui: Fix an error when trying to encode an item with no destination.

Author: sr55

win/CS/HandBrakeWPF/ViewModels/MainViewModel.cs

@@ -1534,6 +1534,15 @@ public bool AddToQueue()
                 return false;
             }
 
+
+            if (!DriveUtilities.HasMinimumDiskSpace(
+                this.Destination,
+                this.userSettingService.GetUserSetting<long>(UserSettingConstants.PauseOnLowDiskspaceLevel)))
+            {
+                this.errorService.ShowMessageBox(Resources.Main_LowDiskspace, Resources.Error, MessageBoxButton.OK, MessageBoxImage.Error);
+                return false;
+            }
+
             // Sanity check the filename
             if (!string.IsNullOrEmpty(this.Destination) && FileHelper.FilePathHasInvalidChars(this.Destination))
             {
@@ -1740,14 +1749,6 @@ public void StartEncode()
                 return;
             }
 
-            if (!DriveUtilities.HasMinimumDiskSpace(
-                this.Destination,
-                this.userSettingService.GetUserSetting<long>(UserSettingConstants.PauseOnLowDiskspaceLevel)))
-            {
-                this.errorService.ShowMessageBox(Resources.Main_LowDiskspace, Resources.Error, MessageBoxButton.OK, MessageBoxImage.Error);
-                return;
-            }
-
             // Create the Queue Task and Start Processing
             if (this.AddToQueue())
             {