Bug 1315407 Fix sdk addon-install r=mossop

MozReview-Commit-ID: FuECBIHE7xR

--HG--
extra : rebase_source : c6be8b33c481364162c36a0a95272fc46a19e996

addon-sdk/source/lib/sdk/addon/installer.js

@@ -64,7 +64,7 @@ exports.install = function install(xpiPath) {
 
   // Order AddonManager to install the addon
   AddonManager.getInstallForFile(file, function(install) {
-    if (install.error != null) {
+    if (install.error == 0) {
       install.addListener(listener);
       install.install();
     } else {