The ornamental design for a merchandisedisplaybase, as shown and described.
FIG. 1 is a perspective view of a merchandise display base showing my new design, the broken lines for illustrative purposes only forming no part of the claimed design;
FIG. 2 is a reduced top plan view thereof;
FIG. 3 is a reduced bottom plan view thereof;
FIG. 4 is a reduced front side elevational view thereof;
FIG. 5 is a reduced rear side elevational view thereof;
FIG. 6 is a reduced left side elevational view thereof; and,