reader/android: add null-check to the log purging code and update vanadium-android to 0.8

Change-Id: I714dcefafbc6d5abd16409fd94d3bbcb285d6d05
diff --git a/android/app/build.gradle b/android/app/build.gradle
index 40bd6b4..54ba5da 100644
--- a/android/app/build.gradle
+++ b/android/app/build.gradle
@@ -89,7 +89,7 @@
     compile 'com.google.android.gms:play-services-analytics:8.3.0'
     compile 'org.apache.commons:commons-csv:1.2'
     compile 'org.apache.commons:commons-io:1.3.2'
-    compile 'io.v:vanadium-android:0.5'
+    compile 'io.v:vanadium-android:0.8'
     compile 'io.v:baku-toolkit:0.3.0'
 
     // Required by baku-toolkit.
diff --git a/android/app/src/main/java/io/v/android/apps/reader/BaseReaderApplication.java b/android/app/src/main/java/io/v/android/apps/reader/BaseReaderApplication.java
index 93917ab..e9178ab 100644
--- a/android/app/src/main/java/io/v/android/apps/reader/BaseReaderApplication.java
+++ b/android/app/src/main/java/io/v/android/apps/reader/BaseReaderApplication.java
@@ -76,12 +76,18 @@
     }
 
     private void deleteOldLogs(File dir) {
-        List<File> logFiles = Arrays.asList(dir.listFiles(new FilenameFilter() {
+        File[] files = dir.listFiles(new FilenameFilter() {
             @Override
             public boolean accept(File file, String s) {
                 return s.startsWith(getLogPrefix());
             }
-        }));
+        });
+
+        if (files == null) {
+            return;
+        }
+
+        List<File> logFiles = Arrays.asList(files);
 
         if (logFiles.size() >= MAX_LOG_COUNT) {
             Collections.sort(logFiles);