bug#38560: 27.0.50; Emacs ignores input events during startup

[Dmitry Gutov]

I have a configuration that takes 1-2 seconds to boot up.

In previous versions (including the latest Emacs 26) it was rarely a
problem because I could always start typing while the configuration
finishes loading (e.g. C-x C-f first-chars-of-file-name).

Emacs 27, however, ignores most of the keystrokes, so when I do that, by
habit, I simply end up in the Scratch buffer with some of the last
characters. E.g. "ile-name" in this example.

In GNU Emacs 27.0.50 (build 29, x86_64-pc-linux-gnu, GTK+ Version 3.24.8)
 of 2019-12-10 built on potemkin
Repository revision: bb8f46d55bb369589ae475e47ad948da88c0d31d
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.12004000
System Description: Ubuntu 19.04

Recent messages:
Loading /home/dgutov/.custom.el (source)...
Loading autorevert...done
Loading help-at-pt...done
Loading /home/dgutov/.custom.el (source)...done
Loading quail/cyrillic...done
Loading /home/dgutov/.emacs.d/site-lisp/.emacs-loaddefs.el (source)...done
Switching to window configuration: nil
Highlight tail mode enabled
For information about GNU Emacs and the GNU system, type C-h C-a.
Package cl is deprecated

Configured using:
 'configure --without-makeinfo'

Configured features:
XPM JPEG TIFF GIF PNG RSVG SOUND GPM DBUS GSETTINGS GLIB NOTIFY INOTIFY
ACL LIBSELINUX GNUTLS LIBXML2 FREETYPE HARFBUZZ M17N_FLT LIBOTF XFT ZLIB
TOOLKIT_SCROLL_BARS GTK3 X11 XDBE XIM MODULES THREADS LIBSYSTEMD JSON
PDUMPER LCMS2 GMP