Fixed a Null Pointer Exception when Wifi Settings is indexing.

Bug: 17335468
Change-Id: I85293e882d90da4a54d4690ffec32fba7101b65e

src/com/android/settings/wifi/AccessPoint.java

@@ -271,10 +271,14 @@ class AccessPoint extends Preference {
                 // set the icon (drawable) to that state's drawable.
                 StateListDrawable sld = (StateListDrawable) context.getTheme()
                         .obtainStyledAttributes(wifi_signal_attributes).getDrawable(0);
+                // If sld is null then we are indexing and therefore do not have access to
+                // (nor need to display) the drawable.
+                if (sld != null) {
                     sld.setState((security != SECURITY_NONE) ? STATE_SECURED : STATE_NONE);
                     drawable = sld.getCurrent();
                     setIcon(drawable);
                 }
+            }
 
             if (drawable != null) {
                 drawable.setLevel(level);