Port or reader state corruption

[sjamaan]

Occasionally, tests ("make check", but also the tests for "scsh-process" and perhaps others) will fail with "unterminated list" errors.

Here are a few examples:

• ​http://ix.io/oFX
• ​http://ix.io/oGm
• ​http://ix.io/oHL
• ​http://paste.call-cc.org/paste?id=2839b340b5ee55b0ace4146993f517b1054f6923

Evan made a ​simple test case which reproducibly causes this error in Musl libc.

The above ix.io errors are reported to be on glibc (Arch Linux), but for unknown reasons the error triggers more often with musl.

[sjamaan]

Fixed! by 691fee5 / 62662bb