fixes #438 belt fan control order

src/kiri/mode/fdm/export.js

@@ -607,7 +607,9 @@ export function fdm_export(print, online, ondone, ondebug) {
         for (pidx=0; pidx<path.length; pidx++) {
             out = path[pidx];
             speedMMM = (out.speed || process.outputFeedrate) * 60; // range
-            fanSpeed = out.fan ?? fanSpeed;
+            if (!isBelt) {
+                fanSpeed = out.fan ?? fanSpeed;
+            }
 
             // hint to controller that we're working on a specific object
             // so that gcode between start/stop comments can be cancelled
@@ -680,13 +682,13 @@ export function fdm_export(print, online, ondone, ondebug) {
             }
 
             // in belt mode, fan can change per segment (for base)
-            // if (isBelt) {
+            if (isBelt) {
                 setTempFanSpeed(out.fan);
-                if (fanSpeed !== lastFanSpeed) {
-                    appendAllSub(gcodeFan);
-                    lastFanSpeed = fanSpeed;
-                }
-            // }
+            }
+            if (fanSpeed !== lastFanSpeed) {
+                appendAllSub(gcodeFan);
+                lastFanSpeed = fanSpeed;
+            }
 
             if (lastp && out.emit) {
                 if (arcDist) {

src/kiri/mode/fdm/prepare.js

@@ -1635,7 +1635,7 @@ function slicePrintPath(print, slice, startPoint, offset, output, opt = {}) {
     print.addPrintPoints(preout, output);
 
     // bridge layer fan change
-    if (!isBelt && preout.length && slice.isBridgeLayer) {
+    if (preout.length && slice.isBridgeLayer) {
         preout[0].fan = Math.round(fanSpeed / 3);
         preout.peek().fan = fanSpeed;
     }