subshell: unexpected command execution

[onlyjob]

Forwarding from ​http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=703741

1. Hide panels (Ctrl+O)
2. Type command kdialog --msgbox "Ops" but do not press enter.
3. Restore panels (Ctrl+O)
4. Note that command prompt is empty
5. Choose directory from panel and try to enter it using keyboard
6. Note that instead of entering directory a command hidden "under panels" was executed.

This is a dangerous situation when command can be accidentally executed.
The following is an original bug report demonstrating loss of data:

####

mc can delete files or execute wierd commands without asking.

How to reproduce:

1. mkdir foo
2. cd foo
3. echo hello world > bar
4. echo something else > other-file
5. mc
6. ctrl+o
7. type "rm -fr bar ", do not press enter
8. ctrl+o, ... hey, how was that file named?
9. pres enter to go to parent directory
10. realize mistake, pres enter again and look at the name of 'other-file'
11. ctrl+o
12. ohh...

I never confirmed the rm command, but file 'bar' is gone...

When mc changes directory in shell, it executes unfinished command. It can
contain anything.

Expected behaviour: Just keep it unchanged and do not change the current
directory, when there is unfinished command.

[andrew_b]

Duplicate of #2110.