Avoid a crash when no compressors are listed. Closes #945

scripts/ssl-enum-ciphers.nse

@@ -1043,7 +1043,9 @@ local function try_protocol(host, port, protocol, upresults)
   results["ciphers"] = ciphers
 
   -- Format the compressor table.
+  if compressors then
     table.sort(compressors)
+  end
   results["compressors"] = compressors
 
   results["cipher preference"] = cipher_pref