Fix NPEs in MenuItem#calculateRenderSize() and MenuItem#getMonitorZoom()

Previously, calculateRenderSize() and getMonitorZoom() of MenuItem used
getMenu() to get some context providing the relevant shell instead of
getParent(). Since that menu may be null when the MenuItem has no submenu
(e.g., PUSH, CHECK styles), an NPE might have been thrown.

This change replaces getMenu().getShell() with getParent().getShell(),
ensuring a valid shell is always used regardless of item type.

Fixes eclipse-platform#2247

Author: ShahzaibIbrahim

bundles/org.eclipse.swt/Eclipse SWT/win32/org/eclipse/swt/widgets/MenuItem.java

@@ -1291,7 +1291,7 @@ GC createNewGC(long hDC, GCData data) {
 }
 
 private int getMonitorZoom() {
-	return getMenu().getShell().getMonitor().zoom;
+	return getParent().getShell().getMonitor().zoom;
 }
 
 private int getMenuZoom() {
@@ -1425,7 +1425,7 @@ LRESULT wmMeasureChild (long wParam, long lParam) {
 }
 
 private Point calculateRenderedTextSize() {
-	GC gc = new GC(this.getMenu().getShell());
+	GC gc = new GC(this.getParent().getShell());
 	String textWithoutMnemonicCharacter = getText().replace("&", "");
 	Point points = gc.textExtent(textWithoutMnemonicCharacter);
 	gc.dispose();