Steps to reproduce:
1. Create a new project
2. Create a new Audio Source in the Hierarchy and select it
3. Expand "3D Sound Settings"
4. Focus on the graph by clicking on it
5. Ensure that zooming in with the scroll wheel works (with and without holding modifier keys, such as Shift for Y-axis and Ctrl for X-axis)
6. Attempt to zoom out with the scroll wheel (with and without holding modifier keys)
7. Create a new Particle System in the Hierarchy and select it
8. In the Inspector, click on "Open Editor..."
9. Repeat steps 5&6

Expected result: User is able to zoom out the entire graph or separate axes if holding down Shift or Ctrl
Actual result: Unable to zoom out entirely.

Reproduced in: 2019.2.13f1, 2019.3.0f2, 2020.1.0a16
Not reproducible in: 2017.4.35f1, 2018.4.14f1, 2019.2.12f1

Note: After passing a certain zoom-in threshold scrolling down will move the graph whereas scrolling up will continue to zoom in
Note 2: Affected components: Audio Source, Particle System, Line Renderer, Trail Renderer