Fixed an illustrious NullPointer bug on Wifi Assistant

+ The class was never instantiated...

Bug: 16543506
Change-Id: I00882df31ee986116b8fa28a54796bb3b20f2e2b
diff --git a/src/com/android/settings/wifi/WifiSettings.java b/src/com/android/settings/wifi/WifiSettings.java
index ccf9fae..e199d3a 100644
--- a/src/com/android/settings/wifi/WifiSettings.java
+++ b/src/com/android/settings/wifi/WifiSettings.java
@@ -729,7 +729,7 @@
     }
 
     private boolean prepareWifiAssistantCard() {
-        if (mWifiAssistantPreference != null) {
+        if (mWifiAssistantPreference == null) {
             mWifiAssistantPreference = new WifiAssistantPreference();
         }