fix(Podfile): Avoid creating an empty Podfile on plugin install

[dpogue]

Platforms affected

iOS

Motivation and Context

Closes GH-1365.

Description

Calling new Podfile(...) will create an empty Podfile in the project if it does not exist. If we don't have any pods to add for a given plugin, we can skip doing anything at all with the Podfile and avoid needlessly creating it.

Note: I moved an if block to do an early return, which de-indented the majority of the code in that function. This PR is easier to review with whitespace changes disabled.

Testing

Tested manually by creating a new project and installing the cordova-plugin-inappbrowser and confirmed that no Podfile was present in the platforms/ios directory.

Checklist

• I've run the tests to see all new and existing tests pass
• If this Pull Request resolves an issue, I linked to the issue in the text above (and used the correct keyword to close issues using keywords)

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 87.50000% with 5 lines in your changes missing coverage. Please review.

Project coverage is 78.35%. Comparing base (fb8eeab) to head (a49ecf2).

Files	Patch %	Lines
lib/Api.js	87.50%	5 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1467   +/-   ##
=======================================
  Coverage   78.35%   78.35%           
=======================================
  Files          16       16           
  Lines        1825     1825           
=======================================
  Hits         1430     1430           
  Misses        395      395           

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[erisu]

Code LGTM