Fix a bunch of crashes discovered by fuzzing cppfront (#1383) #870

Job	Run time
ubu-24 \| g++-14 \| c++2b \| libstdc++ \| ubuntu-24.04	6m 26s
ubu-24 \| g++-13 \| c++2b \| libstdc++ \| ubuntu-24.04	5m 34s
ubu-20 \| g++-10 \| c++20 \| libstdc++ \| ubuntu-20.04	1s
ubu-24 \| clang++-18 \| c++20 \| libstdc++ \| ubuntu-24.04	7m 12s
ubu-24 \| clang++-18 \| c++23 \| libc++-18-dev \| ubuntu-24.04	7m 21s
ubu-22 \| clang++-15 \| c++20 \| libstdc++ \| ubuntu-22.04	5m 40s
ubu-22 \| clang++-15 \| c++20 \| libc++-15-dev \| ubuntu-22.04	5m 55s
ubu-20 \| clang++-12 \| c++20 \| libstdc++ \| ubuntu-20.04	1s
mac-14 \| clang++ \| c++2b \| default \| macos-14	2m 25s
mac-13 \| clang++ \| c++2b \| default \| macos-13	5m 6s
mac-13 \| clang++-15 \| c++2b \| default \| macos-13	7m 10s
win-22 \| cl.exe \| c++latest \| default \| windows-2022	3m 35s
win-22 \| cl.exe \| c++20 \| default \| windows-2022	3m 30s
aggregate-results	0s
	59m 56s

Provide feedback