Load resource from disk before returning None in get_resource()

[JonoYang]

This appears to fix #1362, but I am unsure of how to trigger the issue on command to test for it.

[codecov]

Codecov Report

Merging #1423 into develop will decrease coverage by 60.91%.
The diff coverage is 0%.

@@             Coverage Diff              @@
##           develop    #1423       +/-   ##
============================================
- Coverage    83.65%   22.74%   -60.92%     
============================================
  Files          119      118        -1     
  Lines        13949    13740      -209     
============================================
- Hits         11669     3125     -8544     
- Misses        2280    10615     +8335

Impacted Files	Coverage Δ
src/scancode/resource.py	0% <0%> (-85.7%)	⬇️
src/summarycode/utils.py	0% <0%> (-100%)	⬇️
src/cluecode/copyrights_hint.py	0% <0%> (-100%)	⬇️
src/cluecode/plugin_copyright.py	0% <0%> (-100%)	⬇️
src/cluecode/plugin_email.py	0% <0%> (-100%)	⬇️
src/commoncode/urn.py	0% <0%> (-100%)	⬇️
src/plugincode/output_filter.py	0% <0%> (-100%)	⬇️
src/scancode/plugin_only_findings.py	0% <0%> (-100%)	⬇️
src/commoncode/version.py	0% <0%> (-100%)	⬇️
src/packagedcode/pyrpm/rpmdefs.py	0% <0%> (-100%)	⬇️
... and 99 more

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[codecov]

Codecov Report

Merging #1423 into develop will increase coverage by 0.09%.
The diff coverage is 50%.

@@             Coverage Diff             @@
##           develop    #1423      +/-   ##
===========================================
+ Coverage    83.57%   83.66%   +0.09%     
===========================================
  Files          119      119              
  Lines        14032    14032              
===========================================
+ Hits         11727    11740      +13     
+ Misses        2305     2292      -13

Impacted Files	Coverage Δ
src/scancode/plugin_ignore.py	76.36% <ø> (ø)	⬆️
src/scancode/resource.py	85.98% <50%> (ø)	⬆️
src/scancode/cli.py	78.15% <0%> (+1.04%)	⬆️
src/commoncode/fileutils.py	82.5% <0%> (+1.32%)	⬆️
src/scancode/api.py	94.81% <0%> (+1.48%)	⬆️

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[pombredanne]

@JonoYang I rebased on develop and added a test for the Codebase only in 8fbede6
LGTM... merging!