Fix crash due to missing apps source.

The applications provider has been removed. We should not crash.

Change-Id: I89208a8fa61d8f660344750833f6669ca1b0a9d0
diff --git a/src/com/android/quicksearchbox/SearchableCorpusFactory.java b/src/com/android/quicksearchbox/SearchableCorpusFactory.java
index d3a8367..8acad04 100644
--- a/src/com/android/quicksearchbox/SearchableCorpusFactory.java
+++ b/src/com/android/quicksearchbox/SearchableCorpusFactory.java
@@ -122,7 +122,11 @@
 
     protected Corpus createAppsCorpus(Sources sources) {
         Source appsSource = getAppsSource(sources);
-        return new AppsCorpus(mContext, mConfig, appsSource);
+        if (appsSource == null) {
+            return null;
+        } else {
+            return new AppsCorpus(mContext, mConfig, appsSource);
+        }
     }
 
     protected Corpus createSingleSourceCorpus(Source source) {