The ornamental design for a flagpolebracket, as shown and described.
FIG. 1 is a perspective view of a flag pole bracket showing my new design;
FIG. 2 is a top view thereof;
FIG. 3 is a left view thereof;
FIG. 4 is a front side view thereof;
FIG. 5 is a right side view thereof;
FTG. 6 is a back view thereof; and,
FIG. 7 is a bottom view thereof.
The broken lines shown in the drawings depict portions of the flag pole bracket in which the design is embodied that fonn no part of the claimed design.