Rectifies bug where RPC dump was always using program version 4

CHANGELOG

@@ -25,6 +25,9 @@ o [Windows] Add support for the new loopback behavior in Npcap 0.9983. This
   Adapter to be installed, which was a source of problems for some users.
   [Daniel Miller]
 
+o [NSE] Code improvements in RPC Dump, benefitting NFS-related scripts
+  [nnposter]
+
 o [NSE][GH#1876] XML output from script ssl-cert now includes RSA key modulus
   and exponent [nnposter]
 

nselib/rpc.lua

@@ -2797,8 +2797,6 @@ Helper = {
   RpcInfo = function( host, port )
     local status, result
     local portmap = Portmap:new()
-    local pversion = 4
-    local comm = Comm:new('rpcbind', pversion)
 
     mutex "lock"
 
@@ -2812,7 +2810,9 @@ Helper = {
       return true, nmap.registry[host.ip]['portmapper']
     end
 
+    local pversion = 4
     while pversion >= 2 do
+      local comm = Comm:new('rpcbind', pversion)
       status, result = comm:Connect(host, port)
       if (not(status)) then
         mutex "done"