pw_env_setup: check virtualenv gn target correctly

Check was against the private variable rather than the argument.

Bug: 325
Change-Id: Ib360801b3443f59e82e7340ded43d51c2a5c9289
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/34260
Reviewed-by: Rob Mohr <mohrr@google.com>
Commit-Queue: Armando Montanez <amontanez@google.com>
diff --git a/pw_env_setup/py/pw_env_setup/env_setup.py b/pw_env_setup/py/pw_env_setup/env_setup.py
index 6e17bae..a05663b 100755
--- a/pw_env_setup/py/pw_env_setup/env_setup.py
+++ b/pw_env_setup/py/pw_env_setup/env_setup.py
@@ -219,7 +219,7 @@
             self._cipd_package_file.append(
                 os.path.join(setup_root, 'cipd_setup', 'luci.json'))
             # Only set if no other GN target is provided.
-            if not self._virtualenv_gn_targets:
+            if not virtualenv_gn_target:
                 self._virtualenv_gn_targets.append(
                     virtualenv_setup.GnTarget(
                         '{}#pw_env_setup:python.install'.format(pw_root)))