The ornamental design for a musical instrumentstand, as shown and described.
FIG. 1 is a front left perspective view of a musical instrument stand according to a first embodiment of our design;
FIG. 2 is a front elevation view thereof;
FIG. 3 is a rear elevation view thereof;
FIG. 4 is a right side elevation view thereof;
FIG. 5 is a left side elevation view thereof;
FIG. 6 is a top plan view thereof;
FIG. 7 is a bottom plan view thereof; and,
FIG. 8 is a front left perspective view thereof showing an example use of the musical instrument stand.
The broken lines shown in the drawings are for the purpose of illustrating environmental structure or portions of the musical instrument stand that form no part of the claimed design.