set cliboard placeholder background to invisible by default

avoids showing it in some cases after rotating when it should not be shown

app/src/main/res/layout/clipboard_history_view.xml

@@ -20,6 +20,7 @@
             android:layout_width="wrap_content"
             android:layout_height="wrap_content"
             android:layout_gravity="center"
+            android:visibility="invisible"
             android:text="¯\\_(ツ)_/¯"/>
 
         <org.dslul.openboard.inputmethod.keyboard.clipboard.ClipboardHistoryRecyclerView