Fix Greg's NPE in Downloader

Fixes issue 1579

git-svn-id: http://svn.dmdirc.com/trunk@4498 00569f92-eb28-0410-84fd-f71c24880f

src/com/dmdirc/util/Downloader.java

@@ -159,8 +159,10 @@ public final class Downloader {
         final InputStream input = urlConn.getInputStream();
         final int length = urlConn.getContentLength();
         int current = 0;
-        
-        listener.setIndeterminate(length == -1);
+
+        if (listener != null) {
+            listener.setIndeterminate(length == -1);
+        }
         
         final byte[] buffer = new byte[512];
         int count;