Prevents runtime crashes when the DataGridView or CurrentCell are…

… null.

Fixes #12752

## Root Cause

- The issue occurs because the `NotifyMSAAClient` method is called
without checking if the `DataGridView` instance is `null`. This leads to
a potential `NullReferenceException`.

## Proposed changes

- Add a `null` check for the `DataGridView` instance before calling the
`NotifyMSAAClient` method.
- Adds another `null` check for the `CurrentCell` property before
calling the `PaintGrid` method.
- Add further checks for DataGridView in paint events

## Customer Impact

- Prevents runtime crashes when the `DataGridView` or `CurrentCell` are
null.

## Regression?

- No

## Risk

- Minimal

## Screenshots

### Before

### After

## Test methodology

- Manual testing

## Test environment(s)

- `10.0.100-alpha.1.25064.3`

src/System.Windows.Forms/src/System/Windows/Forms/Controls/DataGridView/DataGridViewCell.cs

@@ -3671,7 +3671,9 @@ internal void PaintWork(Graphics graphics,
             cellStyle,
             advancedBorderStyle,
             paintParts);
-        dataGridView.OnCellPainting(dgvcpe);
+
+        dataGridView?.OnCellPainting(dgvcpe);
+
         if (dgvcpe.Handled)
         {
             return;

src/System.Windows.Forms/src/System/Windows/Forms/Controls/DataGridView/DataGridViewCheckBoxCell.cs

@@ -839,9 +839,9 @@ protected override void OnKeyUp(KeyEventArgs e, int rowIndex)
                 e.Handled = true;
             }
 
-            NotifyMSAAClient(ColumnIndex, rowIndex);
+                NotifyMSAAClient(ColumnIndex, rowIndex);
+            }
         }
-    }
 
     protected override void OnLeave(int rowIndex, bool throughMouseClick)
     {
@@ -967,9 +967,12 @@ private void NotifyUiaClient()
 
     private void NotifyMSAAClient(int columnIndex, int rowIndex)
     {
-        Debug.Assert(DataGridView is not null);
-        Debug.Assert((columnIndex >= 0) && (columnIndex < DataGridView.Columns.Count));
-        Debug.Assert((rowIndex >= 0) && (rowIndex < DataGridView.Rows.Count));
+        if (DataGridView is null ||
+            columnIndex < 0 || columnIndex >= DataGridView.Columns.Count ||
+            rowIndex < 0 || rowIndex >= DataGridView.Rows.Count)
+        {
+            return;
+        }
 
         int visibleRowIndex = DataGridView.Rows.GetRowCount(DataGridViewElementStates.Visible, 0, rowIndex);
         int visibleColumnIndex = DataGridView.Columns.ColumnIndexToActualDisplayIndex(columnIndex, DataGridViewElementStates.Visible);
@@ -1043,7 +1046,11 @@ private Rectangle PaintPrivate(
         bool computeErrorIconBounds,
         bool paint)
     {
+        if(DataGridView is null)
         // Parameter checking.
+        {
+            return Rectangle.Empty;
+        }
 
         // One bit and one bit only should be turned on
         Debug.Assert(paint || computeContentBounds || computeErrorIconBounds);

src/System.Windows.Forms/src/System/Windows/Forms/Controls/DataGridView/DataGridViewRow.cs

@@ -786,9 +786,13 @@ private void BuildInheritedRowHeaderCellStyle(DataGridViewCellStyle inheritedCel
 
     private void BuildInheritedRowStyle(int rowIndex, DataGridViewCellStyle inheritedRowStyle)
     {
+        if (DataGridView is null)
+        {
+            return;
+        }
+
         Debug.Assert(inheritedRowStyle is not null);
         Debug.Assert(rowIndex >= 0);
-        Debug.Assert(DataGridView is not null);
 
         DataGridViewCellStyle? rowStyle = null;
         if (HasDefaultCellStyle)

src/System.Windows.Forms/src/System/Windows/Forms/Controls/DataGridView/DataGridViewRowHeaderCell.cs

@@ -653,6 +653,12 @@ private Rectangle PaintPrivate(
         bool cellSelected = (dataGridViewElementState & DataGridViewElementStates.Selected) != 0;
 
         Debug.Assert(DataGridView is not null);
+
+        if (DataGridView is null)
+        {
+            return Rectangle.Empty;
+        }
+
         if (DataGridView.ApplyVisualStylesToHeaderCells)
         {
             if (cellStyle.Padding != Padding.Empty)

src/System.Windows.Forms/src/System/Windows/Forms/Controls/DataGridView/DataGridViewTextBoxCell.cs

@@ -649,6 +649,11 @@ private Rectangle PaintPrivate(
         bool computeErrorIconBounds,
         bool paint)
     {
+        if (DataGridView is null)
+        {
+            return Rectangle.Empty;
+        }
+
         // Parameter checking. One bit and one bit only should be turned on.
         Debug.Assert(paint || computeContentBounds || computeErrorIconBounds);
         Debug.Assert(!paint || !computeContentBounds || !computeErrorIconBounds);