The ornamental design for a frenchdoorsauna, as shown and described.
FIG. 1 is a top left side exterior perspective view of the sauna of the present invention;
FIG. 2 is a cut away left side interior perspective view thereof, taken from line 2-2 in FIG. 1;
FIG. 3 is a front exterior elevation view thereof; and,
FIG. 4 is a left side exterior elevation view thereof.
The rear elevation view, right side elevation view and a bottom plan view have been omitted as they do not form a portion of the claimed design. The broken lines shown in the drawings are directed to environment, are for informational purposes only, and form no part of the claimed design.