Fix file descriptor leaks in the hist builtin (#336)

This commit fixes two file descriptor leaks in the hist built-in.
The bugfix for the first file descriptor leak was backported from
ksh2020. See:
https://github.com/att/ast/issues/872
73bd61b5

Reproducer:
  $ echo no
  $ hist -s no=yes

The second file descriptor leak occurs after a substitution error
in the hist built-in (this leak wasn't fixed in ksh2020).
Reproducer:
  $ echo no
  $ ls /proc/$$/fd
  $ hist -s no=yes
  $ hist -s no=yes
  $ ls /proc/$$/fd

src/cmd/ksh93/bltins/hist.c:
- Close leftover file descriptors when an error occurs and after
  'hist -s' runs a command.

src/cmd/ksh93/tests/builtins.sh:
- Add two regression tests for both of the file descriptor leaks.

NEWS

@@ -9,6 +9,9 @@ Any uppercase BUG_* names are modernish shell bug IDs.
   special floating point constants Inf and NaN so that $((inf)) and $((nan))
   refer to the variables by those names as the standard requires. (BUG_ARITHNAN)
 
+- Fixed two file descriptor leaks in the hist builtin that occurred when
+  the -s flag ran a command or encountered an error.
+
 2021-11-14:
 
 - Fixed: ksh crashed after unsetting .sh.match and then matching a pattern.