[gnome-builder] rustup: only wait if the subprocess spawned

[Christian Hergert <chergert src gnome org>]

commit b4d997a956ca410865942eaafef961fafa7b5af5
Author: Christian Hergert <chergert redhat com>
Date:   Sun Mar 19 06:12:41 2017 -0700

    rustup: only wait if the subprocess spawned

 plugins/rustup/rustup_plugin/__init__.py |    3 +--
 1 files changed, 1 insertions(+), 2 deletions(-)
---
diff --git a/plugins/rustup/rustup_plugin/__init__.py b/plugins/rustup/rustup_plugin/__init__.py
index 5bdf0f8..5a05458 100644
--- a/plugins/rustup/rustup_plugin/__init__.py
+++ b/plugins/rustup/rustup_plugin/__init__.py
@@ -325,11 +325,10 @@ class RustupInstaller(Ide.Transfer):
 
         try:
             sub_process = launcher.spawn()
+            sub_process.wait_async(cancellable, self._wait_cb, task)
         except Exception as ex:
             task.return_error(GLib.Error(message=repr(ex)))
 
-        sub_process.wait_async(cancellable, self._wait_cb, task)
-
     def _read_line_cb(self, data_stream, result, cancellable):
         try:
             line, length = data_stream.read_line_finish_utf8(result)