BUG: Fix warnings and possible UB in `VariadicInputsImageFilter::SetInputsImpl`

Summary

Avoid returning a temporary value from the function.

Rationale

Spotted on Debian Testing with GCC 9.2.1:

/otb/Modules/Core/Functor/include/otbVariadicInputsImageFilter.h: In instantiation of 'auto otb::VariadicInputsImageFilter<TOuptut, TInputs>::SetInputsImpl(Tuple&, std::index_sequence<Is ...>) [with Tuple = std::tuple<otb::VectorImage<float, 2>*>; long unsigned int ...Is = {0}; TOuptut = otb::VectorImage<float, 2>; TInputs = {otb::VectorImage<float, 2>}; std::index_sequence<Is ...> = std::integer_sequence<long unsigned int, 0>]':
/otb/Modules/Core/Functor/include/otbVariadicInputsImageFilter.h:125:5:   required from 'void otb::VariadicInputsImageFilter<TOuptut, TInputs>::SetInputs(TInputs* ...) [with TOuptut = otb::VectorImage<float, 2>; TInputs = {otb::VectorImage<float, 2>}]'
/otb/Modules/Applications/AppIndices/app/otbRadiometricIndices.cxx:260:46:   required from here
/otb/Modules/Core/Functor/include/otbVariadicInputsImageFilter.h:148:91: warning: returning temporary initializer_list does not extend the lifetime of the underlying array [-Winit-list-lifetime]
  148 |     return std::initializer_list<int>{(this->template SetInput<Is>(std::get<Is>(t)), 0)...};
      |                                                                                           ^

Copyright

The copyright owner is Laurențiu Nicola (CS ROMANIA) and has signed the ORFEO ToolBox Contributor License Agreement.

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