throw illegalArg error on null location

some url shorteners sometimes return 302s without
a location header (bah.) throw illegal arg exception
rather than NPE from URI.resolve

Author: jloomis

src/main/java/com/ning/http/util/AsyncHttpProviderUtils.java

@@ -218,6 +218,8 @@ public final static String getHost(URI uri) {
     }
 
     public final static URI getRedirectUri(URI uri, String location) {
+        if(location == null)
+            throw new IllegalArgumentException("URI " + uri + " was redirected to null location");
         URI newUri = uri.resolve(location);
 
         String scheme = newUri.getScheme();