Fix panic when Wasm input is too large

[tomaka]

The allocator makes sure to the grow memory for its own metadata, but doesn't necessarily grow the memory enough for the allocated data to fit.

[github-actions]

twiggy diff report

Difference in .wasm size before and after this pull request.

---

 Delta Bytes │ Item
─────────────┼──────────────────────────────────────────────────────────────────────────
         +93 ┊ smoldot::executor::host::HostVmPrototype::run_vectored::h86121a026f2add57
         +93 ┊ smoldot::executor::host::HostVmPrototype::run_vectored::hbb493c299af20e51
         +93 ┊ smoldot::executor::host::HostVmPrototype::run_vectored::he720b7a3dc7b06b5
         +91 ┊ smoldot::executor::host::HostVmPrototype::run_vectored::ha1a07bab01fc5d71
         +77 ┊ smoldot::executor::host::HostVmPrototype::run_vectored::h8595c20e12de4f03
         +75 ┊ smoldot::executor::host::HostVmPrototype::run_vectored::h35f29a13e3b7f384
         +75 ┊ smoldot::executor::host::HostVmPrototype::run_vectored::hdcf84ffc0c960bc8
         +70 ┊ smoldot::executor::host::HostVmPrototype::run_vectored::h1175c97123f4cbc4
         +32 ┊ data[0]
          +6 ┊ nom::combinator::all_consuming::h8f748b8b1a1d61d2
          -4 ┊ core::result::Result<T,E>::unwrap::h516f9048a2509f4c
          +1 ┊ elem[0]
        +760 ┊ Σ [12 Total Rows]