Fix bottom navigation crash bug on global layout.

When updating the menu item spacing for the Chrome Home bottom
navigation menu, we were checking the length of a potentially null array
so a null check has been added.

Bug: 796185
Change-Id: I1382aace706ad2b0ffb13e9c84bf78efc7284ceb
Reviewed-on: https://chromium-review.googlesource.com/848242
Commit-Queue: Troy Hildebrandt <thildebr@chromium.org>
Reviewed-by: Matthew Jones <mdjones@chromium.org>
Cr-Commit-Position: refs/heads/master@{#526747}

chrome/android/third_party/widget_bottomsheet_base/java/src/org/chromium/chrome/browser/widget/bottomsheet/base/BottomNavigationMenuView.java

@@ -225,7 +225,7 @@ public class BottomNavigationMenuView extends LinearLayout implements MenuView {
      * @param layoutHeight Height of the navigation menu's container.
      */
     public void updateMenuItemSpacingForMinWidth(int layoutWidth, int layoutHeight) {
-        if (mButtons.length == 0) return;
+        if (mButtons == null || mButtons.length == 0) return;
 
         int menuWidth = Math.min(layoutWidth, layoutHeight);
         if (menuWidth != mMenuWidth) {