The ornamental design for a lampbracket, as shown and described.
FIG. 1 is a first perspective view of a lamp bracket showing the claimed new design;
FIG. 2 is a second 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 plane view thereof;
FIG. 8 is a bottom plane view thereof; and,
FIG. 9 is a perspective view of thereof in an environment in which it may be used.
The broken lines immediately adjacent to the claimed portions are boundaries, all other broken lines are environmental structures; all the broken lines form no part of the claimed design.