Use safe version of os.path.isfile

[philippjfr]

Fixes #985

[codecov]

Codecov Report

Merging #986 into master will increase coverage by 0.09%.
The diff coverage is 76.47%.

@@            Coverage Diff             @@
##           master     #986      +/-   ##
==========================================
+ Coverage    85.7%   85.79%   +0.09%     
==========================================
  Files          99       99              
  Lines       11239    11246       +7     
==========================================
+ Hits         9632     9649      +17     
+ Misses       1607     1597      -10

Impacted Files	Coverage Δ
panel/pane/media.py	70.73% <100%> (-0.2%)	⬇️
panel/pane/image.py	78.51% <100%> (-0.06%)	⬇️
panel/pane/vtk/vtk.py	53.43% <100%> (+1.05%)	⬆️
panel/io/save.py	77.35% <50%> (+1.43%)	⬆️
panel/pane/base.py	89.74% <50%> (-1.8%)	⬇️
panel/util.py	89.26% <78.57%> (+2.3%)	⬆️
panel/interact.py	76.07% <0%> (+2.5%)	⬆️

---

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 aed6293...3a1d016. Read the comment docs.