Hard-wrapped commands are displayed incorrectly after READLINE_LINE is changed

[Lauri Ranta]

Configuration Information [Automatically generated, do not change]:
Machine: x86_64
OS: darwin14.5.0
Compiler: clang
Compilation CFLAGS:  -DPROGRAM='bash' -DCONF_HOSTTYPE='x86_64' 
-DCONF_OSTYPE='darwin14.5.0' -DCONF_MACHTYPE='x86_64-apple-darwin14.5.0' 
-DCONF_VENDOR='apple' -DLOCALEDIR='/usr/local/Cellar/b$
uname output: Darwin Lauris-iMac-3.local 14.0.0 Darwin Kernel Version 14.0.0: 
Fri Sep 19 00:26:44 PDT 2014; root:xnu-2782.1.97~2/RELEASE_X86_64 x86_64
Machine Type: x86_64-apple-darwin14.5.0

Bash Version: 4.3
Patch Level: 42
Release Status: release

With for example `bind -x '"\ea":READLINE_LINE='` and `PS1='$ '`, if the width 
of a shell window is 20 characters so that the 30 character command

    $ aaaaaaaaaaaaaaaaaa
    aaaaaaaaaaaa

is displayed on two lines, after pressing `\ea`, the command is displayed as

    $ aaaaaaaaaaaaaaaaaa
    $

if the point is on the second line or as

    $
    aaaaaaaaaaaa

if the point is on the first line.