In any case there would have been little likelihood of Madeleine wandering outside of her own accord. Greater minds disagree but there it is.
To begin with she had woken on a previous night and cried at length rather than actively attempting to seek her parents - that being a perfectly normal reaction for a 3-4 year old in the circumstances.
Perhaps if she had been on home ground and knew exactly where to find her parents, she may have attempted to do so. Here things were very different.
It is hard to know exactly what her sense of geography was, but there is nothing to say that she would have had much of an idea of where her parents were in relation to the apartment (if indeed she imagined them to be within walking distance. Who knows where she thought they were).
Even if she knew them to be close by, this was unfamiliar territory, which she covered only a few times. Perhaps a 50 yard journey on home turf, covered regularly, would have been easy to navigate - a school run, for example. But would she ever have traversed the direct route from the apartment to the tapas with her parents during the day? Probably not. So how would she imagine that she could figure it out herself alone in pitch black?
The notion of being drawn to the lights of the restaurant and following her nose shows an adult perception of the situation, not hers.
If she had been sufficiently distressed as to leave the apartment and venture into the night (she wasn't scared of the dark?), she would most probably have been crying as well, and may have been heard.
All in all a most unlikely possibility.