--drop-down mode sometimes opens new windows rather than showing/hiding existing instance

Submitted by Bharadwaj Raju

Assigned to Igor @f2404

Description

I have set the command "xfce4-terminal --drop-down" bound the Ctrl+` key to "xfce4-terminal --drop-down".

For the most part it works out: I press the shortcut and the correct instance of the terminal drops down.

However, when I by mistake press the shortcut multiple times, it fails to detect the existing instance and instead opens a fresh drop-down terminal. At that point I have to start a normal terminal and kill the new xfce4-terminal --drop-down process.

Steps to Reproduce

Make sure an xfce4-terminal --drop-down process is already running, and maybe type something into it to identify this instance.
Press the shortcut multiple times quickly.
You will find that there are now 2 instances of xfce4-terminal --drop-down. Verify by:
```
 $ for i in $(pgrep xfce4-terminal); do ps -fp "$i"; done
```

Software Versions

OS: Arch Linux Version: xfce4-terminal 0.8.7.4 (Xfce 4.12)

Version: 0.8.7.4