Fix input idx issue when some inputs are not set.

aidge_core/aidge_export_aidge/templates/graph_ctor/_set_input.jinja

-{%- for input in inputs if input[0] %}
+{# NOTE: Trying a shorter notation like {%- for input in inputs if input[0] %}
+will mess up loop.index as the input set up at None will not increment ! #}
+{%- for input in inputs %}
+{%- if input[0] %}
 {{input[0]}}->addChild({{name}}, {{input[1]}}, {{loop.index - 1}}); {# NOTE: loop.index begin at 1 #}
+{%- endif %}
 {%- endfor %}