TUI crashes when clicking on non-deterministic branch

When you get a non-deterministic branch and click it in the TUI, you get a crash with the following error message:

╭────────────────────────────────── Traceback (most recent call last) ──────────────────────────────────╮
│ /nix/store/3q2jq2933abmcn832icdj8fd00pzcxc4-python3.10-pyk-0.1.434/lib/python3.10/site-packages/pyk/k │
│ cfg/tui.py:400 in on_graph_chunk_selected                                                             │
│                                                                                                       │
│   397 │   │   elif message.chunk_id.startswith('ndbranch_'):                                          │
│   398 │   │   │   self._selected_chunk = None                                                         │
│   399 │   │   │   node_source, node_target, *_ = message.chunk_id[8:].split('_')                      │
│ ❱ 400 │   │   │   source_id = int(node_source)                                                        │
│   401 │   │   │   target_id = int(node_target)                                                        │
│   402 │   │   │   ndbranch = single(self._kcfg.ndbranches(source_id=source_id, target_id=targe        │
│   403 │   │   │   self.query_one('#node-view', NodeView).update(ndbranch)                             │
│                                                                                                       │
│ ╭─────────────────────────────────── locals ───────────────────────────────────╮                      │
│ │           _ = ['9']                                                          │                      │
│ │     message = Selected()                                                     │                      │
│ │ node_source = ''                                                             │                      │
│ │ node_target = '8'                                                            │                      │
│ │        self = APRProofViewer(title='APRProofViewer', classes={'-dark-mode'}) │                      │
│ ╰──────────────────────────────────────────────────────────────────────────────╯                      │
╰───────────────────────────────────────────────────────────────────────────────────────────────────────╯
ValueError: invalid literal for int() with base 10: ''

Reproduction:

• clone https://github.com/smart-transaction/test-contract
• checkout branch hjort
• kevm foundry-kompile --verbose && kevm foundry-prove --test PinataTest.testA0 --smt-timeout 300 --smt-retry-limit 4 --verbose
• open with kevm foundry-view-kcfg
• locate a non-deterministic branch (I see one after node 8).
• click it

Start in pyk/kcfg/tui.py at on_graph_chunk_selected, especially the ndbranch_ handling around line 400. Reproduce the failure with the listed test-contract checkout and kevm commands, then open the KCFG TUI and click the non-deterministic branch after node 8. Done means selecting that branch no longer crashes with a ValueError.