Improve fix wrong code generation if EN/ENO are used in FBD/LD/SFC

Commit c9915bc6 "Fix wrong code generation if EN/ENO are used in
FBD/LD/SFC" caused following backtrace in some cases:

File "/home/developer/WorkData/PLC/beremiz/beremiz/PLCGenerator.py", line 476, in GenerateProgram
self.GeneratePouProgram(pou_name)
File "/home/developer/WorkData/PLC/beremiz/beremiz/PLCGenerator.py", line 258, in GeneratePouProgram
program = pou_program.GenerateProgram(pou)
File "/home/developer/WorkData/PLC/beremiz/beremiz/PLCGenerator.py", line 1713, in GenerateProgram
self.ComputeProgram(pou)
File "/home/developer/WorkData/PLC/beremiz/beremiz/PLCGenerator.py", line 997, in ComputeProgram
eno_var = self.GetUsedEno(body, connections)
File "/home/developer/WorkData/PLC/beremiz/beremiz/PLCGenerator.py", line 929, in GetUsedEno
for invar in blk.inputVariables.getvariable():
File "/home/developer/WorkData/PLC/beremiz/beremiz/xmlclass/xmlclass.py", line 1363, in getattrMethod
return DefaultElementClass.__getattribute__(self, name)
<type 'exceptions.AttributeError'>: 'inOutVariable' object has no attribute 'inputVariables'

<?xml version='1.0' encoding='utf-8'?>
<PyFile xmlns:xhtml="http://www.w3.org/1999/xhtml" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
  <variables/>
  <globals>
    <xhtml:p><![CDATA[import threading, time

MyT = None
Stop = False

def StartLog():
    global MyT
    MyT=threading.Thread(target = DoLog)
    MyT.start()

def DoLog():
    global Stop
    while not Stop:
        PLCObject.LogMessage("Python side Logging (PLC is %s)"%PLCObject.PLCStatus)
        time.sleep(0.3)

def StopLog():
    global MyT,Stop
    Stop=True

_runtime_init.append(StartLog)
_runtime_cleanup.append(StopLog)
]]></xhtml:p>
  </globals>
  <init>
    <xhtml:p><![CDATA[]]></xhtml:p>
  </init>
  <cleanup>
    <xhtml:p><![CDATA[]]></xhtml:p>
  </cleanup>
  <start>
    <xhtml:p><![CDATA[]]></xhtml:p>
  </start>
  <stop>
    <xhtml:p><![CDATA[]]></xhtml:p>
  </stop>
</PyFile>