Fix crash if LD input contact isn't connected

Traceback (most recent call last):
File "/home/developer/WorkData/PLC/beremiz/beremiz/BeremizIDE.py", line 339, in OnMethod
obj.CTR.CallMethod('_'+meth)
File "/home/developer/WorkData/PLC/beremiz/beremiz/ProjectController.py", line 1996, in CallMethod
getattr(self, method)()
File "/home/developer/WorkData/PLC/beremiz/beremiz/ProjectController.py", line 1134, in _Build
IECGenRes = self._Generate_SoftPLC()
File "/home/developer/WorkData/PLC/beremiz/beremiz/ProjectController.py", line 746, in _Generate_SoftPLC
if self._Generate_PLC_ST():
File "/home/developer/WorkData/PLC/beremiz/beremiz/ProjectController.py", line 763, in _Generate_PLC_ST
self._getIECgeneratedcodepath())
File "/home/developer/WorkData/PLC/beremiz/beremiz/PLCControler.py", line 456, in GenerateProgram
self.ProgramChunks = GenerateCurrentProgram(self, self.Project, errors, warnings)
File "/home/developer/WorkData/PLC/beremiz/beremiz/PLCGenerator.py", line 1762, in GenerateCurrentProgram
generator.GenerateProgram()
File "/home/developer/WorkData/PLC/beremiz/beremiz/PLCGenerator.py", line 478, in GenerateProgram
self.GeneratePouProgram(pou_name)
File "/home/developer/WorkData/PLC/beremiz/beremiz/PLCGenerator.py", line 260, in GeneratePouProgram
program = pou_program.GenerateProgram(pou)
File "/home/developer/WorkData/PLC/beremiz/beremiz/PLCGenerator.py", line 1718, in GenerateProgram
self.ComputeProgram(pou)
File "/home/developer/WorkData/PLC/beremiz/beremiz/PLCGenerator.py", line 1028, in ComputeProgram
self.GenerateBlock(instance, block_infos, body, None)
File "/home/developer/WorkData/PLC/beremiz/beremiz/PLCGenerator.py", line 1144, in GenerateBlock
expression = self.ComputeExpression(body, connections, executionOrderId > 0)
File "/home/developer/WorkData/PLC/beremiz/beremiz/PLCGenerator.py", line 1373, in ComputeExpression
paths = self.GeneratePaths(connections, body, order, to_inout)
File "/home/developer/WorkData/PLC/beremiz/beremiz/PLCGenerator.py", line 1344, in GeneratePaths
elif isinstance(result[0], list):
IndexError: list index out of range


Close #70

{
    "version": 2,
    "controller": {},
    "workers": [
        {
            "type": "router",
            "options": {
                "pythonpath": [
                    ".."
                ]
            },
            "realms": [
                {
                    "name": "Automation",
                    "roles": [
                        {
                            "name": "anonymous",
                            "permissions": [
                                {
                                    "uri": "",
                                    "match": "prefix",
                                    "allow": {
                                        "call": true,
                                        "register": true,
                                        "publish": true,
                                        "subscribe": true
                                    },
                                    "disclose": {
                                        "caller": false,
                                        "publisher": false
                                    },
                                    "cache": true
                                }
                            ]
                        }
                    ]
                }
            ],
            "transports": [
                {
                    "type": "websocket",
                    "debug": true,
                    "endpoint": {
                        "type": "tcp",
                        "port": 8888
                    },
                    "url": "ws://127.0.0.1:8888/",
                    "serializers": [
                        "msgpack",
                        "json"
                    ]
                }
            ]
        }
    ]
}