libnativebridge: fix a potential null deref

Caught by the static analyzer:
> art/libnativebridge/native_bridge.cc:239:40: warning: Access to field
'version' results in a dereference of a null pointer (loaded from
variable 'callbacks') [clang-analyzer-core.NullDereference]

Bug: None
Test: TreeHugger
Change-Id: Ia0eb0daac6ee3b07b9ffd615cec9f0a431de2900
diff --git a/libnativebridge/native_bridge.cc b/libnativebridge/native_bridge.cc
index 7600780..46a05a2 100644
--- a/libnativebridge/native_bridge.cc
+++ b/libnativebridge/native_bridge.cc
@@ -233,10 +233,10 @@
             // Store the handle for later.
             native_bridge_handle = handle;
           } else {
-            callbacks = nullptr;
-            dlclose(handle);
             ALOGW("Unsupported native bridge API in %s (is version %d not compatible with %d)",
                   nb_library_filename, callbacks->version, NAMESPACE_VERSION);
+            callbacks = nullptr;
+            dlclose(handle);
           }
         } else {
           dlclose(handle);