Prevent GCode load during slicing

- Issue MatterHackers/MCCentral#5453
Crash after switching to 3D GCode view while slicing

MatterControlLib/ApplicationView/ApplicationController.cs

@@ -2606,6 +2606,8 @@ namespace MatterHackers.MatterControl
 			// Slice
 			bool slicingSucceeded = false;
 
+			printer.ViewState.SlicingItem = true;
+
 			await this.Tasks.Execute("Slicing".Localize(), printer, async (reporter, cancellationToken) =>
 			{
 				slicingSucceeded = await Slicer.SliceItem(
@@ -2616,6 +2618,8 @@ namespace MatterHackers.MatterControl
 					cancellationToken);
 			});
 
+			printer.ViewState.SlicingItem = false;
+
 			// Skip loading GCode output if slicing failed
 			if (!slicingSucceeded)
 			{

MatterControlLib/ApplicationView/BedConfig.cs

@@ -369,6 +369,7 @@ namespace MatterHackers.MatterControl
 		internal void EnsureGCodeLoaded()
 		{
 			if (this.LoadedGCode == null
+				&& !this.Printer.ViewState.SlicingItem
 				&& File.Exists(this.EditContext?.GCodeFilePath(this.Printer)))
 			{
 				UiThread.RunOnIdle(async () =>

MatterControlLib/ApplicationView/PrinterViewState.cs

@@ -185,5 +185,7 @@ namespace MatterHackers.MatterControl
 				UserSettings.Instance.set(UserSettingsKey.SelectedObjectPanelWidth, minimumValue.ToString());
 			}
 		}
+
+		public bool SlicingItem { get; set; }
 	}
 }