Bug 1429045 - Fix http status test to return in the right places, r=Ms2ger

This was a regression from bug 1396534

MozReview-Commit-ID: 9Yfdo2rGqVZ

testing/web-platform/tests/http/resources/securedimage.py

@@ -6,10 +6,12 @@ def main(request, response):
     if "authorization" not in request.headers:
         response.status = 401
         response.headers.set("WWW-Authenticate", "Basic")
+        return
     else:
         auth = request.headers.get("Authorization")
         if auth != "Basic dGVzdHVzZXI6dGVzdHBhc3M=":
             response.set_error(403, "Invalid username or password - " + auth)
+            return
 
     response.status = 301
     response.headers.set("Location", image_url)