feat: interpolate CAL from current saved file

main.c

@@ -567,7 +567,7 @@ update_frequencies(void)
     frequencies[i] = start + span * i / (sweep_points - 1) * 100;
 
   if (cal_auto_interpolate)
-    cal_interpolate(0);
+    cal_interpolate(lastsaveid);
 
   update_marker_index();
   

plot.c

@@ -1373,12 +1373,11 @@ draw_cal_status(void)
   ili9341_fill(0, y, 10, 6*YSTEP, 0x0000);
   if (cal_status & CALSTAT_APPLY) {
     char c[3] = "C0";
+    c[1] += lastsaveid;
     if (cal_status & CALSTAT_INTERPOLATED)
       c[0] = 'c';
-    if (active_props == &current_props)
+    else if (active_props == &current_props)
       c[1] = '*';
-    else
-      c[1] += lastsaveid;
     ili9341_drawstring_5x7(c, x, y, 0xffff, 0x0000);
     y += YSTEP;
   }