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'

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PROJECT_NAME;%(Project Name)s;;;;;;;;;;;;;;
VERSION_OF_REFERENCEFILE;%(EDE file version)d;;;;;;;;;;;;;;
TIMESTAMP_OF_LAST_CHANGE;%(Current Time)s;;;;;;;;;;;;;;
AUTHOR_OF_LAST_CHANGE;%(Project Author)s;;;;;;;;;;;;;;
VERSION_OF_LAYOUT;2.1;;;;;;;;;;;;;;
#mandatory;mandatory;mandatory;mandatory;mandatory;optional;optional;optional;optional;optional;optional;optional;optional;optional;optional;optional
#keyname;device obj.-instance;object-name;object-type;object-instance;description;present-value-default;min-present-value;max-present-value;settable;supports COV;hi-limit;low-limit;state-text-reference;unit-code;vendor-specific-address