Remove many ERROR outputs from non-debug NSE output

scripts/http-userdir-enum.nse

@@ -41,7 +41,7 @@ categories = {"auth", "intrusive"}
 
 portrule = shortport.http
 
-
+local function fail (err) return stdnse.format_output(false, err) end
 
 action = function(host, port)
 
@@ -52,21 +52,13 @@ action = function(host, port)
 
   -- speedy exit if no usernames
   if(#usernames == 0) then
-    if(nmap.debugging() > 0) then
-      return "Didn't find any users to test (should be in nselib/data/usernames.lst)"
-    else
-      return nil
-    end
+    return fail("Didn't find any users to test (should be in nselib/data/usernames.lst)")
   end
 
   -- Check what response we get for a 404
   local result, result_404, known_404 = http.identify_404(host, port)
   if(result == false) then
-    if(nmap.debugging() > 0) then
-      return "ERROR: " .. result_404
-    else
-      return nil
-    end
+    return fail(result_404)
   end
 
   -- Check if we can use HEAD requests
@@ -93,11 +85,7 @@ action = function(host, port)
   -- Check for http.pipeline error
   if(results == nil) then
     stdnse.debug1("http.pipeline returned nil")
-    if(nmap.debugging() > 0) then
-      return "ERROR: http.pipeline returned nil"
-    else
-      return nil
-    end
+    return fail("http.pipeline returned nil")
   end
 
   local found = {}