fix: reapply new batch after `#commit` (#18186)

Fixes a regression of #18170 (not released yet therefore no changeset).
`current_batch` is nulled out if the `#commit` rebases other branches,
and that can lead to nullpointers down the line.

No test right now but it's part of getting the failing SvelteKit test
passing.

packages/svelte/src/internal/client/reactivity/batch.js

@@ -363,6 +363,8 @@ export class Batch {
 		// TODO fix the underlying cause, otherwise this will likely regress when non-async mode is removed
 		if (async_mode_flag && !batches.has(this)) {
 			this.#commit();
+			// Rebases can activate other batches or null it out, therefore restore the new one here
+			current_batch = next_batch;
 		}
 
 		// Edge case: During traversal new branches might create effects that run immediately and set state,