The ornamental design for a flexiblestand for a fan, as shown and described.
FIG. 1 is a right side front perspective view of a flexible stand for a fan showing my new design;
FIG. 2 is a right side rear perspective view thereof;
FIG. 3 is a front 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 rear elevation view thereof; and,
FIG. 7 is an enlarged top plan view thereof.
The broken line showing of the fan and the stand in alternate positions is included for the purpose of illustrating environmental structure and forms no part of the claimed design.