fix some dumb (nonfatal) crashes in the editor with nothing loaded

OpenRA.Editor/Form1.Designer.cs

@@ -429,7 +429,6 @@
             this.surface1.Size = new System.Drawing.Size(783, 727);
             this.surface1.TabIndex = 5;
             this.surface1.Text = "surface1";
-            this.surface1.Click += new System.EventHandler(this.OnSurfaceClicked);
             // 
             // saveFileDialog
             // 

OpenRA.Editor/Form1.cs

@@ -35,7 +35,13 @@ namespace OpenRA.Editor
 
 			Rules.LoadRules(Game.modData.Manifest, new Map());
 
-			surface1.AfterChange += MakeDirty;
+			surface1.AfterChange += OnMapChanged;
+		}
+
+		void OnMapChanged()
+		{
+			MakeDirty();
+			pmMiniMap.Image = Minimap.AddStaticResources(surface1.Map, Minimap.TerrainBitmap(surface1.Map, true));
 		}
 
 		void MakeDirty() { dirty = true; }
@@ -390,11 +396,6 @@ namespace OpenRA.Editor
 			pb.Show();
 		}
 
-		private void OnSurfaceClicked(object sender, EventArgs e)
-		{
-			pmMiniMap.Image = Minimap.AddStaticResources(surface1.Map, Minimap.TerrainBitmap(surface1.Map, true));
-		}
-
         private void mnuMinimapToPNG_Click(object sender, EventArgs e)
         {
             try

OpenRA.Editor/Surface.cs

@@ -87,6 +87,8 @@ namespace OpenRA.Editor
 		{
 			base.OnMouseWheel(e);
 
+			if (Map == null) return;
+
 			Zoom *= e.Delta > 0 ? 4.0f / 3.0f : .75f;
 
 			Invalidate();
@@ -114,6 +116,8 @@ namespace OpenRA.Editor
 		{
 			base.OnMouseMove(e);
 
+			if (Map == null) return;
+
 			var oldMousePos = MousePos;
 			MousePos = new int2(e.Location);
 
@@ -332,6 +336,8 @@ namespace OpenRA.Editor
 		{
 			base.OnMouseDown(e);
 
+			if (Map == null) return;
+
 			if (!IsPanning)
 			{
 				if (e.Button == MouseButtons.Right) Erase();