Snap selection to grid: fixed a problem that could cause a crash if geometry got removed by snapping it to the grid

Source/Core/Editing/EditMode.cs

@@ -260,6 +260,10 @@ namespace CodeImp.DoomBuilder.Editing
 		// Script events
 		public virtual bool OnScriptRunBegin() { return true; }
 		public virtual void OnScriptRunEnd() { }
+
+		// This should be called by global actions (i.e. that are not part of an editing mode) when they changed map elements,
+		// so that the mode can react to it (for example by rebuilding a blockmap)
+		public virtual void OnMapElementsChanged() { }
 		
 		#endregion
 	}

Source/Core/General/MapManager.cs

@@ -2643,6 +2643,9 @@ namespace CodeImp.DoomBuilder
 				undoredo.WithdrawUndo();
 			}
 
+			// Let the current editing mode know that we changed something
+			General.Editing.Mode.OnMapElementsChanged();
+
 			// Done
 			General.Interface.RedrawDisplay();
 			Cursor.Current = Cursors.Default;

Source/Plugins/BuilderModes/ClassicModes/LinedefsMode.cs

@@ -1217,6 +1217,16 @@ namespace CodeImp.DoomBuilder.BuilderModes
 			return base.OnCopyBegin();
 		}
 
+		/// <summary>
+		/// If map elements have changed the blockmap needs to be recreated.
+		/// </summary>
+		public override void OnMapElementsChanged()
+		{
+			base.OnMapElementsChanged();
+
+			CreateBlockmap();
+		}
+
 		//mxd
 		private void RenderComment(Linedef l)
 		{

Source/Plugins/BuilderModes/ClassicModes/SectorsMode.cs

@@ -1596,6 +1596,16 @@ namespace CodeImp.DoomBuilder.BuilderModes
 			General.Interface.RedrawDisplay();
 		}
 
+		/// <summary>
+		/// If map elements have changed the blockmap needs to be recreated.
+		/// </summary>
+		public override void OnMapElementsChanged()
+		{
+			base.OnMapElementsChanged();
+
+			CreateBlockmap();
+		}
+
 		//mxd
 		public override void OnViewSelectionNumbersChanged(bool enabled)
 		{

Source/Plugins/BuilderModes/ClassicModes/VerticesMode.cs

@@ -759,7 +759,17 @@ namespace CodeImp.DoomBuilder.BuilderModes
 			
 			return base.OnCopyBegin();
 		}
-		
+
+		/// <summary>
+		/// If map elements have changed the blockmap needs to be recreated.
+		/// </summary>
+		public override void OnMapElementsChanged()
+		{
+			base.OnMapElementsChanged();
+
+			CreateBlockmap();
+		}
+
 		#endregion
 
 		#region ================== Actions