[gnome-builder] rustup: check for valid output from rustup

[Christian Hergert <chergert src gnome org>]

commit 724ec1a30ee013ab3d6c5e4fe5e07d048e2f802d
Author: Christian Hergert <chergert redhat com>
Date:   Sun Mar 19 05:32:11 2017 -0700

    rustup: check for valid output from rustup
    
    We could get nothing back if there was an error in here somewhere.

 plugins/rustup/rustup_plugin/__init__.py |    5 +++--
 1 files changed, 3 insertions(+), 2 deletions(-)
---
diff --git a/plugins/rustup/rustup_plugin/__init__.py b/plugins/rustup/rustup_plugin/__init__.py
index 56d9a67..5bdf0f8 100644
--- a/plugins/rustup/rustup_plugin/__init__.py
+++ b/plugins/rustup/rustup_plugin/__init__.py
@@ -127,8 +127,9 @@ class RustupApplicationAddin(GObject.Object, Ide.ApplicationAddin):
                 sub_process = launcher.spawn()
 
                 _, stdout, stderr = sub_process.communicate_utf8(None, None)
-                self.rustup_executable = rustup_bin
-                break
+                if stdout:
+                    self.rustup_executable = rustup_bin
+                    break
             except GLib.Error as e:
                 pass
         if self.rustup_executable is None: