The ornamental design for a vial pump with flag, as shown.
FIG. 1 is a front elevational view of the first embodiment of a vial pump with flag showing my new design, the undisclosed top, bottom and side views are not part of the claimed design;
FIG. 2 is a front elevational view of a second embodiment of a vial pump with flag showing my new design, the undisclosed top, bottom, and side views are not part of the claimed design;
FIG. 3 is a front elevational view of a third embodiment of a vial pump with flag showing my new design, the undisclosed top, bottom, and sides are not part of the claimed design; and,
FIG. 4 is a front elevational view of a fourth embodiment of a vial pump with flag showing my new design, the undisclosed top, bottom, and side views are not part of the claimed design.