I claim the ornamental design for a girder, as shown and described.
FIG. 1 is an isometric view of a girder, showing the new design;
FIG. 2 is a left side view of the girder of FIG. 1;
FIG. 3 is a right side view of the girder of FIG. 1;
FIG. 4 is a top view of the girder of FIG. 1;
FIG. 5 is a rear view of the girder of FIG. 1;
FIG. 6 is a bottom view of the girder of FIG. 1; and,
FIG. 7 is a front view of the girder of FIG. 1.
The girder is shown with a symbolic break in its length. The appearance of any portion of the girder between the break lines forms no part of the claimed design.