[MacPlatform] Fix message dialog parenting issue in VCS checkout.

Checkout messages were shown below other dialogs. This was introduced
with:
#4478

Author: mkrueger

main/src/addins/MacPlatform/Dialogs/MacAlertDialogHandler.cs

@@ -240,12 +240,17 @@ public bool Run (AlertDialogData data)
 							NSApplication.SharedApplication.StopModal ();
 						});
 
-						// pass parent and not alert so that the Runloop will change
-						// and processing will stop until the sheet is closed.
-						// If we pass alert, then it will run until a second alert is created
-						// which will be shown as a dialog and then the runloop changes and
-						// processing stops
-						NSApplication.SharedApplication.RunModalForWindow (parent);
+						if (IdeApp.Workbench.RootWindow?.Visible == true) {
+							// pass parent and not alert so that the Runloop will change
+							// and processing will stop until the sheet is closed.
+							// If we pass alert, then it will run until a second alert is created
+							// which will be shown as a dialog and then the runloop changes and
+							// processing stops
+							NSApplication.SharedApplication.RunModalForWindow (parent);
+						} else {
+							// fixes message dialog below other dialogs issue when no main window is present (at start)
+							NSApplication.SharedApplication.RunModalForWindow (alert.Window);
+						}
 					}
 				}
 

main/src/core/MonoDevelop.Ide/MonoDevelop.Ide.ProgressMonitoring/MessageDialogProgressMonitor.cs

@@ -40,7 +40,7 @@ public class MessageDialogProgressMonitor: ProgressMonitor
 		bool hideWhenDone;
 		bool showDetails;
 
-		public ProgressDialog ProgressDialog { get => dialog; }
+		public ProgressDialog ProgressDialog => dialog;
 
 		public MessageDialogProgressMonitor (): this (false)
 		{