Fix updating of bitmap_drawn() when drawing

Fixes high CPU when nothing is happening.

src/conio/bitmap_con.c

@@ -854,6 +854,7 @@ bitmap_draw_vmem(int sx, int sy, int ex, int ey, struct vmem_cell *fill)
 		int coff = vmem_cell_offset(vm, 0, 0);
 		int foff = 0;
 		for (size_t vy = 0; vy < vheight; vy++) {
+			int coff = vmem_cell_offset(vm, sx - 1, sy - 1 + vy);
 			for (size_t vx = 0; vx < vwidth; vx++) {
 				bitmap_drawn[coff] = fill[foff++];
 				coff = vmem_next_offset(vm, coff);
@@ -867,6 +868,7 @@ bitmap_draw_vmem(int sx, int sy, int ex, int ey, struct vmem_cell *fill)
 			int coff = vmem_cell_offset(vm, sx - 1, sy - 1 + vy);
 			for (size_t vx = 0; vx < vwidth; vx++) {
 				bitmap_drawn[coff] = fill[foff++];
+				coff = vmem_next_offset(vm, coff);
 				calc_charstate(&bs, &fill[vy * vwidth + vx], &charstate[vx], sx + vx, sy + vy);
 			}
 			// Draw the characters...