Fixed a bug when reversing y-axis order in Density/Ridges plot in Histogram dialog

[Vitalis95]

Fixes #6978
Replaces PR #7644
@rdstern @lloyddewit @N-thony ,this PR fixes the error when trying to reverse y-axis order in Density/Ridges plot

[lloyddewit]

This change is much smaller than the changes in PR #7644 (which was merged and then reverted in PR #7739). What's the reason?

[Vitalis95]

@lloyddewit, this the only change I made from my side (removing that line which is the one causing the bug). I never made any other change to this dialog.

[lloyddewit]

@lloyddewit, this the only change I made from my side (removing that line which is the one causing the bug). I never made any other change to this dialog.

@Vitalis95 Thanks for the explanation. I'm not quite sure where the changes in the previous PR came from (parallel changes on the same file in master?). But these are reverted anyway so it's not important. I'm happy to approve.

@rdstern over to you for testing ...

[rdstern]

When I return to the dialogue I get (each time)

In addition, when I did reverse on the y-axis I got the following:

[Vitalis95]

@rdstern the developer error is now sorted. The error "Discreet value supplied to continuous scale" is because month_abbr is factor

[N-thony]

@rdstern the developer error is now sorted. The error "Discreet value supplied to continuous scale" is because month_abbr is factor

@rdstern please have look

[rdstern]

I think the code is now better, so I am approving.
At a later stage we do need to be able to complete the discrete scales. However, I found the best way to reverse the months on the plot given in the issue is perhaps to reverse the levels in the factor first!