fix: guard against double-unsubscribe removing wrong subscriber in cache.ts (#4252)

fix: guard against double-unsubscribe removing wrong subscriber

When the unsubscribe function returned by `subscribe` was called more
than once, `subs.indexOf(callback)` returned -1, causing
`subs.splice(-1, 1)` to silently remove the last subscriber in the
array instead of doing nothing.

Fix by checking `index >= 0` before mutating the array, using the same
O(1) swap-and-pop pattern already used in `subscribe-key.ts`.

Signed-off-by: tomohiro86 <supersonic.dps@gmail.com>
Co-authored-by: Tomohiro Yamada <tomohiro.yamada@TomohironoMacBook-Air.local>

Author: tomohiro86

src/_internal/utils/cache.ts

@@ -56,7 +56,14 @@ export const initCache = <Data = any>(
       subscriptions[key] = subs
 
       subs.push(callback)
-      return () => subs.splice(subs.indexOf(callback), 1)
+      return () => {
+        const index = subs.indexOf(callback)
+        if (index >= 0) {
+          // O(1): swap with the last element and pop
+          subs[index] = subs[subs.length - 1]
+          subs.pop()
+        }
+      }
     }
     const setter = (key: string, value: any, prev: any) => {
       provider.set(key, value)