Check if public namespace has already been initialized

There is no point in reading/loading the list of public
libraries once public namespace is already initialized.

Change-Id: I5a53c46bb57b8de241ba521a6321c12e94a76476
diff --git a/libnativeloader/native_loader.cpp b/libnativeloader/native_loader.cpp
index 33d5b62..9a24714 100644
--- a/libnativeloader/native_loader.cpp
+++ b/libnativeloader/native_loader.cpp
@@ -105,6 +105,13 @@
   }
 
   void Initialize() {
+    // Once public namespace is initialized there is no
+    // point in running this code - it will have no effect
+    // on the current list of public libraries.
+    if (initialized_) {
+      return;
+    }
+
     std::vector<std::string> sonames;
     const char* android_root_env = getenv("ANDROID_ROOT");
     std::string root_dir = android_root_env != nullptr ? android_root_env : "/system";