There is no need to take the null char into account when copying
mutated data with memcpy in AST fuzzer.
Change-Id: I78530c3679a31f252d2eaebd6de2a1261d346a57
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/59449
Auto-Submit: Vasyl Teliman <vasniktel@gmail.com>
Kokoro: Kokoro <noreply+kokoro@google.com>
Commit-Queue: Vasyl Teliman <vasniktel@gmail.com>
Reviewed-by: Ben Clayton <bclayton@google.com>