Summary

Fixes an undocumented (?) issue with scaling ViewBoxes with locked aspect ratio when the mouse is over the axes.

How to reproduce the issue

1. Run the code:

import numpy as np
import pyqtgraph as pg

plot = pg.plot(np.random.normal(scale=10, size=100))
plot.disableAutoRange()
plot.setAspectLocked()

pg.exec()

2. Position the mouse pointer on the vertical axis. Scroll the mouse wheel down a few clicks. The graph will zoom out.
3. Move the mouse cursor to the horizontal axis and try scrolling the mouse wheel. The graph will jump back to its original state and stop responding.
4. Move the mouse pointer to the graph and scroll the mouse wheel upwards a few clicks. The graph will jump back to the zoomed out state and start to zoom in.
5. Move the mouse pointer to the horizontal axis and try scrolling the mouse wheel. The image will jump up and stop responding.

Bugs Found And Changes Made

1. The ViewBox._resetTarget function had a wrong logic inside, which caused ViewBox to jump between different zoom states.
   Fixed by removing unnecessary if-condition.
   1.1 The function argument 'force' has become useless, so it has been removed from the signature and from calls using it.
2. The ViewBox.scaleBy function treated x and y axes differently.
   A check has been added to determine which axis is the primary axis, and the secondary axis is scaled accordingly.

Results

When trying to reproduce the issue, there are no zoom jumps and mouse wheel works as expected.