FindBugs error: manage error condition for Gerrit passwd for Git/HTTP

When using Git over HTTP(/S) we need to transparently generate
a Gerrit HTTP password. Should this fail we need to block the
redirect to the Git over HTTP endpoint and just return an error.

Change-Id: I62180c9eb6e9e9206510a63c9b7987a5c2c64696

github-oauth/src/main/java/com/googlesource/gerrit/plugins/github/oauth/OAuthGitFilter.java

diff --git a/github-oauth/src/main/java/com/googlesource/gerrit/plugins/github/oauth/OAuthGitFilter.java b/github-oauth/src/main/java/com/googlesource/gerrit/plugins/github/oauth/OAuthGitFilter.java
index cd8b32e..91f3b86 100644
--- a/github-oauth/src/main/java/com/googlesource/gerrit/plugins/github/oauth/OAuthGitFilter.java
+++ b/github-oauth/src/main/java/com/googlesource/gerrit/plugins/github/oauth/OAuthGitFilter.java
@@ -150,7 +150,12 @@
         gerritPassword =
             generateRandomGerritPassword(username, httpRequest, httpResponse,
                 chain);
-        httpResponse.sendRedirect(getRequestPathWithQueryString(httpRequest));
+        if (Strings.isNullOrEmpty(gerritPassword)) {
+          httpResponse.sendError(SC_FORBIDDEN,
+              "Unable to generate Gerrit password for Git Basic-Auth");
+        } else {
+          httpResponse.sendRedirect(getRequestPathWithQueryString(httpRequest));
+        }
         return;
       }