[MRG] load surf data in view_surf

[jeromedockes]

otherwise if it is provided as a file path the function fails e.g.

from nilearn import datasets, plotting
fsaverage = datasets.fetch_surf_fsaverage()
plotting.view_surf(fsaverage['pial_left'], fsaverage['sulc_left'],
                   cmap='Greys', threshold=None, symmetric_cmap=False)

[codecov]

Codecov Report

Merging #2057 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #2057      +/-   ##
==========================================
+ Coverage   94.97%   94.97%   +<.01%     
==========================================
  Files         141      141              
  Lines       18254    18256       +2     
==========================================
+ Hits        17336    17338       +2     
  Misses        918      918

Impacted Files	Coverage Δ
nilearn/plotting/html_surface.py	100% <100%> (ø)	⬆️
nilearn/plotting/tests/test_html_surface.py	100% <100%> (ø)	⬆️

---

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[codecov]

Codecov Report

Merging #2057 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #2057      +/-   ##
==========================================
+ Coverage   94.98%   94.98%   +<.01%     
==========================================
  Files         141      141              
  Lines       18298    18299       +1     
==========================================
+ Hits        17380    17381       +1     
  Misses        918      918

Impacted Files	Coverage Δ
nilearn/plotting/html_surface.py	100% <100%> (ø)	⬆️
nilearn/plotting/tests/test_html_surface.py	100% <100%> (ø)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 2dde3f9...1f6fa47. Read the comment docs.

[kchawla-pi]

Hey, this is cool. Would you document the reason for this PR in the first comment, so there is a record of the problem or even better file an issue and link it here?

[kchawla-pi]

I was about to merge it, we should add Fix in whats_new .

[kchawla-pi]

WHy did none of the tests catch this earlier? Do we have a test that catches this now?

[jeromedockes]

Do we have a test that catches this now?

yes it is added in test_html_surface.py in this pr

[jeromedockes]

@kchawla-pi do you have more comments or can we merge?