Public API LTAS analysis runs a classic spectrogram analysis

I just ran a LTAS analysis with PBS jobs on Datarmor, and got this error:

> numpy._core._exceptions._ArrayMemoryError: Unable to allocate 1.21 TiB for an array with shape (165888000000, 1) and data type float64

It appears that I somehow made the `export_analysis` module run a classic Spectrogram analysis despite the `Analysis` having a non-null `nb_ltas_time_bins` attribute.