The ornamental design for handgun holster, as shown and described.
FIG. 1 is a perspective view of a handgun holster showing my new design;
FIG. 2 is a bottom perspective view thereof;
FIG. 3 is a front elevational view thereof;
FIG. 4 is a rear elevational view thereof;
FIG. 5 is a left side elevational view thereof;
FIG. 6 is a right side elevational view thereof;
FIG. 7 is a top plan view thereof;
FIG. 8 is a bottom plan view thereof; and,
FIG. 9 is a perspective view showing the handgun holster with an attached clip.
The broken line showing fasteners and attached clip in FIG. 1-FIG. 6, FIG. 8, and FIG. 9 is included for the purpose of illustrating environmental structure and forms no part of the claimed design.