odd focus/resize behavior

## I'm submitting a…

[x] Bug

[ ] Feature Request

[ ] Documentation Request

[ ] Other (Please describe in detail)

## Current Behavior

Configuring the mouse wheel for resizing windows, focus_follows_mouse disabled

```
focus_follows_mouse no
bindsym --whole-window Mod1+Control+button4 resize grow height 10 px or 1 ppt; resize grow width 10 px or 1 ppt
bindsym --whole-window Mod1+Control+button5 resize shrink width 10 px or 1 ppt; resize shrink height 10 px or 1 ppt
```

## Expected Behavior

1. Open multiple windows in split or floating.
2. Hoover the mouse over the **focused** window and then 'Mod1+Control+*mousewheel*' grows/shrinks the window as expected.

## Reproduction Instructions

1. Open multiple windows in split or floating.
2. Hoover the mouse over a **non focused** window and then 'Mod1+Control+*mousewheel*'
- Mod1+Control+button4 grows the *focused* window
- Mod1+Control+button5 shrinks the window where the mouse is *hoovering*

This is quite inconsistent/inconvinient, on split windows, either mouse direction will only shrink the windows where the mouse is hoovering when it does not have focus. On floating it feels even more weird.

## Environment

Output of `i3 --moreversion 2>&-`:

i3 version: 

Binary i3 version:  4.17.1 (2019-08-30, branch "4.17.1") © 2009 Michael Stapelberg and contributors

Running i3 version: 4.17.1 (2019-08-30, branch "4.17.1") (pid 16527)

Loaded i3 config: /home/ct/.i3/config (Last modified: So 17 Nov 2019 17:36:35 CET, 52175 seconds ago)


The i3 binary you just called: /usr/local/bin/i3

The i3 binary you are running: i3

The 3 lines for configuring focus/mousewheel above added to the default config cause this behavior.

Logfile URL:

n/a can provide one on demand.

- Linux Distribution & Version:

  * Debian 9.11

  * i3 build from source

- Are you using a compositor (e.g., xcompmgr or compton):

  * bug happens under compton as well without