fix: guard learning map pinch zoom state

src/pages/LearningMapsPage.tsx

@@ -60,6 +60,7 @@ function getMidpoint(a: Point, b: Point) {
 }
 
 function clampScale(value: number) {
+  if (!Number.isFinite(value)) return 1
   return Math.min(5, Math.max(1, value))
 }
 
@@ -246,12 +247,20 @@ export function LearningMapsPage() {
       const [first, second] = Array.from(pointersRef.current.values())
       const distance = getDistance(first, second)
       const midpoint = getMidpoint(first, second)
-      const nextScale = clampScale(pinchRef.current.scale * (distance / pinchRef.current.distance))
+      const pinch = pinchRef.current
+
+      if (!Number.isFinite(distance) || distance <= 0 || pinch.distance <= 0) {
+        return
+      }
+
+      const nextScale = clampScale(pinch.scale * (distance / pinch.distance))
+      const deltaX = midpoint.x - pinch.midpoint.x
+      const deltaY = midpoint.y - pinch.midpoint.y
 
       setScale(nextScale)
       setOffset((current) => ({
-        x: current.x + (midpoint.x - pinchRef.current!.midpoint.x) * 0.8,
-        y: current.y + (midpoint.y - pinchRef.current!.midpoint.y) * 0.8,
+        x: current.x + deltaX * 0.8,
+        y: current.y + deltaY * 0.8,
       }))
       pinchRef.current.midpoint = midpoint
       return