Don't allocate in exception handler

[jsturtevant]

Partially addresses: #1118

The test run with out this change fails with memory allocation:

assertion `left == right` failed: Full error: GuestAborted(8, "panicked at /home/jstur/.rustup/toolchains/1.89-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/alloc/src/alloc.rs:438:13:\nmemory allocation of 182 bytes failed")
  left: 8
 right: 15

[ludfjig]

nice!