fix: don't try to add to a null milliseconds counter

Signed-off-by: Octol1ttle <l1ttleofficial@outlook.com>

src/main/java/ru/octol1ttle/flightassistant/computers/TimeComputer.java

@@ -12,7 +12,7 @@ public class TimeComputer implements ITickableComputer {
      */
     public float deltaTime;
     public boolean highlight;
-    public Float millis = 0.0f;
+    public Float millis;
     private Float prevMillis;
     private float highlightMillis;
 
@@ -36,6 +36,9 @@ public void tick() {
         if (mc.isInSingleplayer() && mc.isPaused()) {
             return;
         }
+        if (millis == null) {
+            millis = 0.0f;
+        }
         millis += deltaMS;
 
         if (millis - highlightMillis > HIGHLIGHT_SWITCH_THRESHOLD) {