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

# the platform name (PyV8, smjs, Mozilla, IE6, Opera, Safari etc.)
platform = ''  # to be updated by app, on compile

# a dictionary of module override names (platform-specific)
overrides = {}  # to be updated by app, on compile

# the remote path for loading modules
loadpath = None

stacktrace = None

appname = None


def setloadpath(lp):
    global loadpath
    loadpath = lp


def setappname(an):
    global appname
    appname = an


def getloadpath():
    return loadpath


def addoverride(module_name, path):
    overrides[module_name] = path


def addstack(linedebug):
    JS("""
        if (pyjslib.bool((sys.stacktrace === null))) {
            sys.stacktrace = new pyjslib.List([]);
        }
        sys.stacktrace.append(linedebug);
    """)


def popstack():
    JS("""
        sys.stacktrace.pop()
    """)


def printstack():
    JS("""
        var res = '';

        var __l = sys.stacktrace.__iter__();
        try {
            while (true) {
                var l = __l.next();
                res +=  ( l + '\\n' ) ;
            }
        } catch (e) {
            if (e != pyjslib.StopIteration) {
                throw e;
            }
        }

        return res;
    """)