[woff2] Support `hmtx' reconstruction when `glyf' is untransformed. `reconstruct_hmtx' requires `info->x_mins' and `info->num_glyphs' to reconstruct the hmtx table. In case glyf is not transformed, we call `get_x_mins' which does the necessary work. * src/sfnt/sfwoff2.c (get_x_mins): New function. (reconstruct_font): Call get_x_mins.