The ornamental design for a holder for a hairdryer, as shown and described.
FIG. 1 is an environmental perspective view of a holder for a hair dryer in accordance with my design;
FIG. 2 is a perspective view of the holder for a hair dryer;
FIG. 3 is a top plan view of the holder for a hair dryer of FIG. 2;
FIG. 4 is a front elevational view thereof;
FIG. 5 is a side elevational view as viewed from the right side of FIG. 4, with the left side elevational view being a mirror image thereof;
FIG. 6 is a rear elevational view thereof; and,
FIG. 7 is a bottom plan view thereof.
The broken lines showing a hair dryer in FIG. 1 illustrate environment. The remaining broken lines illustrate portions of the holder for a hair dryer. None of the broken lines form part of the claimed design.