Better handle null delegates by returning instead of CHECK()

ui/accessibility/platform/ax_platform_node_win.cc

Index: ui/accessibility/platform/ax_platform_node_win.cc
diff --git a/ui/accessibility/platform/ax_platform_node_win.cc b/ui/accessibility/platform/ax_platform_node_win.cc
index 15fc2119f192e9c21b866e8c9127bdfc7e79546c..ca9ef23a165e5e247c421f5fa581a03b3787fa71 100644
--- a/ui/accessibility/platform/ax_platform_node_win.cc
+++ b/ui/accessibility/platform/ax_platform_node_win.cc
@@ -1381,7 +1381,6 @@ STDMETHODIMP AXPlatformNodeWin::get_columnHeaderCells(
   *n_column_header_cells = 0;
   auto* table = GetTable();
   if (!table) {
-    NOTREACHED();
     return S_FALSE;
   }
 
@@ -1438,7 +1437,6 @@ STDMETHODIMP AXPlatformNodeWin::get_rowHeaderCells(IUnknown*** cell_accessibles,
   *n_row_header_cells = 0;
   auto* table = GetTable();
   if (!table) {
-    NOTREACHED();
     return S_FALSE;
   }