Add AndroidSonarClient.getInstanceIfInitialized()

Summary:
Sometimes you want to get the sonar client without necessarily wanting to initialize it, for example if you don't have a context object, but still want to get hold of a particular plugin object.
Adds a getInstance method that returns null if not initialized.

Reviewed By: passy

Differential Revision: D9154423

fbshipit-source-id: 65cb46684bc35d9a953dbd958c7cf72aba0015e2

android/src/main/java/com/facebook/sonar/android/AndroidSonarClient.java

@@ -48,6 +48,13 @@ public final class AndroidSonarClient {
     return SonarClientImpl.getInstance();
   }
 
+  public static synchronized SonarClient getInstanceIfInitialized() {
+    if (!sIsInitialized) {
+      return null;
+    }
+    return SonarClientImpl.getInstance();
+  }
+
   static void checkRequiredPermissions(Context context) {
     // Don't terminate for compatibility reasons. Not all apps have ACCESS_WIFI_STATE permission.
     for (String permission : REQUIRED_PERMISSIONS) {