fixed CB-11078 Empty string for BackgroundColor preference crashes application

This closes #316

test/androidTest/src/org/apache/cordova/test/CordovaActivityTest.java

@@ -42,4 +42,7 @@ public class CordovaActivityTest extends BaseCordovaIntegrationTest {
         String onPageFinishedUrl = testActivity.onPageFinishedUrl.take();
         assertEquals(MainTestActivity.START_URL, onPageFinishedUrl);
     }
+    protected void createViews() {
+        assertTrue(testView instanceof SystemWebView);
+    }
 }

test/res/xml/config.xml

@@ -35,6 +35,7 @@
     <preference name="useBrowserHistory" value="true" />
     <preference name="exit-on-suspend" value="false" />
     <preference name="showTitle" value="true" />
+    <preference name="BackgroundColor" value="" />
     <feature name="Activity">
         <param name="android-package" value="org.apache.cordova.test.ActivityPlugin" />
     </feature>