~lattis/muon#78: SIGSEGV on empty meson.build

Steps to reproduce:

: > meson.build

~/t/muon-segfault> muon setup build

fish: Job 1, 'muon setup build' terminated by signal SIGSEGV (Address boundary error)

Muon version details:

muon v0.1.0-a7c6a84
meson compatibility version 0.63.99
enabled features:
  libcurl
  libpkgconf
  libarchive

I'm currently on arm64 and am using muon-meson-git from AUR. I haven't tested on x86_64.