Added some error checking to CredEnuerateA() railgun call

modules/post/windows/gather/credentials/enum_cred_store.rb

@@ -178,7 +178,17 @@ class MetasploitModule < Msf::Post
     credentials = []
     #call credenumerate to get the ptr needed
     adv32 = session.railgun.advapi32
+    begin
       ret = adv32.CredEnumerateA(nil,0,4,4)
+    rescue Rex::Post::Meterpreter::RequestError => e
+      print_error("This module requires WinXP or higher")
+      print_error("CredEnumerateA() failed: #{e.class} #{e}")
+      ret = nil
+    end
+    if ret.nil?
+      count = 0
+      arr_len = 0
+    else
       p_to_arr = ret["Credentials"].unpack("V")
       if is_86
         count = ret["Count"]
@@ -187,6 +197,7 @@ class MetasploitModule < Msf::Post
         count = ret["Count"] & 0x00000000ffffffff
         arr_len = count * 8
       end
+    end
 
     #tell user what's going on
     print_status("#{count} credentials found in the Credential Store")