Fix zerodivision errors in pdfviewer when windows are extremely small

[jmoraleda]

This fixes the error:

  File "/Users/mysuser/virtualenv/cytopar/lib/python3.11/site-packages/wx/lib/pdfviewer/viewer.py", line 217, in LoadFile
    self.CalculateDimensions()      # to get initial visible page range
    ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/myuser/virtualenv/cytopar/lib/python3.11/site-packages/wx/lib/pdfviewer/viewer.py", line 371, in CalculateDimensions
    self.frompage = int(min(self.y0/self.Ypagepixels, self.numpages-1))
                            ~~~~~~~^~~~~~~~~~~~~~~~~
ZeroDivisionError: division by zero

which can be observed by trying to resize a window containing a pdfviewer to extremely small sizes.

I remark that this PR expands on a previous PR of mine a few years ago, which handled the case when window client sizes were exactly zero on initialization #1519 but did not consider cases where window client sizes were very small, which would, through rounding from floating point to int, also result in ZeroDivision errors as shown above.

[jmoraleda]

@swt2c Hello Scott. I noticed you just merged #2470 . I wonder if you would be able to review and merge this one too. It is on the same module and related to visualization too. I discovered both issues together. Thank you.

[jmoraleda]

I am closing this PR in favor of #2480