emacs: Fix digits input after completion (re: 16e4824c, e8b3274a)

Immediately after tab-completing the name of a directory, it is
not possible to type digits after the slash; ksh eats them as it
parses them as a menu selection for a nonexistent menu.

Reproducer:
$ mkdir -p emacstest/123abc
$ cd emacste[tab]123abc

Actual results:
$ cd emacstest/abc

Expected results:
$ cd emacstest/123abc

Workarounds are to press a non-numeric key followed by backspace,
or hit [tab] again to get a list of options.

Originally reported by Arnon Weinberg, 2012-12-23 07:15:19 UTC, at:
https://bugzilla.redhat.com/889745

The fix had been partially backported from ksh 93v- by AT&T
(16e4824c), which made things worse, so it was reverted (e8b3274a).
This commit backports a slightly edited version of the complete
fix. Thanks to @JohnoKing for finding the correct code. Discussion:
https://github.com/ksh93/ksh/issues/198#issuecomment-820178514

src/cmd/ksh93/edit/emacs.c: escape():
- Backport the fix for this bug that was implemented in ksh 93v-
  alpha 2013-10-10. Immediately after a slash, do not stay in "\"
  mode (file name completion) and reset the tab count.

src/cmd/ksh93/tests/pty.sh:
- Test the fix.

Resolves: https://github.com/ksh93/ksh/issues/198

src/cmd/ksh93/tests/pty.sh

@@ -786,5 +786,16 @@ r ^:test-2: echo asdf\r\n$
 r ^asdf\r\n$
 !
 
+# err_exit #
+((SHOPT_ESH)) && mkdir -p emacstest/123abc && VISUAL=emacs tst $LINENO <<"!"
+L autocomplete stops numeric input
+# https://github.com/ksh93/ksh/issues/198
+
+d 15
+p :test-1:
+w cd emacste\t123abc
+r ^:test-1: cd emacstest/123abc\r\n$
+!
+
 # ======
 exit $((Errors<125?Errors:125))