[U-Boot] CTRL-C hangs after "hush: fix segfault on syntax error"

[Stephen Warren]

Rabin,

With 128059b926b3 "hush: fix segfault on syntax error" applied, I find
that if I press CTRL-C at the U-Boot prompt, U-Boot hangs. If I revert
that commit, CTRL-C works fine (prints CTRL-C and returns to the command
prompt).

I'm testing on real HW (rpi_b board), although I don't expect the exact
HW matters. This issue doesn't reproduce with sandbox, since CTRL-C now
seems to just execute the binary rather than being handled by U-Boot shell.