DocsUI: Don't crash on invalid window sizes.

Our layout code asserts when passed an (invalid) width of 0.  The assert
is unnecessary as we already handle this situation by always laying out
the content pane with a column count of at least 1.

Also, per Steve, bump the minimum column count in grid mode to 2.

BUG=27150284

Change-Id: I8aa87beaaf4907ef5248999d0c590deef732589f

packages/DocumentsUI/src/com/android/documentsui/dirlist/DirectoryFragment.java

@@ -98,7 +98,6 @@ import com.android.documentsui.model.RootInfo;
 import com.android.documentsui.services.FileOperationService;
 import com.android.documentsui.services.FileOperationService.OpType;
 import com.android.documentsui.services.FileOperations;
-
 import com.google.common.collect.Lists;
 
 import java.lang.annotation.Retention;
@@ -406,9 +405,9 @@ public class DirectoryFragment extends Fragment
         int cellMargin = 2 * getResources().getDimensionPixelSize(R.dimen.grid_item_margin);
         int viewPadding = mRecView.getPaddingLeft() + mRecView.getPaddingRight();
 
-        assert(mRecView.getWidth() > 0);
-
-        int columnCount = Math.max(1,
+        // RecyclerView sometimes gets a width of 0 (see b/27150284).  Clamp so that we always lay
+        // out the grid with at least 2 columns.
+        int columnCount = Math.max(2,
                 (mRecView.getWidth() - viewPadding) / (cellWidth + cellMargin));
 
         return columnCount;