CB-12683: improved error messaging for when a plugin doesn't have pac…

[stevengill]

…kage.json

Platforms affected

What does this PR do?

What testing has been done on this change?

Checklist

• Reported an issue in the JIRA database
• Commit message follows the format: "CB-3232: (android) Fix bug with resolving file paths", where CB-xxxx is the JIRA ID & "android" is the platform affected.
• Added automated test coverage as appropriate for this change.

[codecov-io]

Codecov Report

Merging #548 into master will decrease coverage by 0.02%.
The diff coverage is 50%.

@@            Coverage Diff             @@
##           master     #548      +/-   ##
==========================================
- Coverage   83.34%   83.31%   -0.03%     
==========================================
  Files          65       65              
  Lines        5163     5167       +4     
  Branches     1029     1030       +1     
==========================================
+ Hits         4303     4305       +2     
- Misses        860      862       +2

Impacted Files	Coverage Δ
cordova-lib/src/plugman/fetch.js	83.75% <50%> (-0.87%)	⬇️

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[purplecabbage]

+1