OpenDelta: No NPE please

Happens very very rarely

src/eu/chainfire/opendelta/UpdateService.java

@@ -483,6 +483,7 @@ public class UpdateService extends Service implements OnNetworkStateListener,
         if (latestBuild != null) {
             File found = null;
             File[] files = new File(mConfig.getPathBase()).listFiles();
+            if (files != null && files.length > 0) {
                 for (File file : files) {
                     String currName = file.getName();
                     if (file.isFile() && currName.endsWith(".part")) {
@@ -492,6 +493,7 @@ public class UpdateService extends Service implements OnNetworkStateListener,
                             file.delete(); // remove old .part files
                     }
                 }
+            }
             if (found != null) {
                 long total = mPrefs.getLong(PREF_DOWNLOAD_SIZE, 1500000000L /* 1.5 GB */);
                 final long current = found.length();