Fix #2090: avoid bang bang operator in networkinterceptor

[prudhvir3ddy]

Explanation

removed bang bang operator which may null pointer exception though current code got null check but this is just a better way of coding and making use of kotlin higher order function . fixes #2090

Checklist

• The PR title starts with "Fix #bugnum: ", followed by a short, clear summary of the changes. (If this PR fixes part of an issue, prefix the title with "Fix part of #bugnum: ...".)
• The PR explanation includes the words "Fixes #bugnum: ..." (or "Fixes part of #bugnum" if the PR only partially fixes an issue).
• The PR follows the style guide.
• The PR does not contain any unnecessary auto-generated code from Android Studio.
• The PR is made from a branch that's not called "develop".
• The PR is made from a branch that is up-to-date with "develop".
• The PR's branch is based on "develop" and not on any other branch.
• The PR is assigned to an appropriate reviewer in both the Assignees and the Reviewers sections.

[anandwana001]

@prudhvir3ddy
We recommend to follow few points:

1. PR title Fix #bugnum: short description
2. Branch naming, please check our wiki here - https://github.com/oppia/oppia-android/wiki#instructions-for-making-a-code-change
3. As per the last point in the above checklist, you can also mention me or @rt4914 for review in the PR description, until you get the Reviewer/Assignee section access.

[prudhvir3ddy]

@anandwana001 anyhow my branch will be deleted after this merge right ?

[anandwana001]

@prudhvir3ddy The branch is from your fork, so it's up to you to delete or not. As per the naming, you can choose a descriptive naming with all small caps with - to separate, from your next PR's.

[aggarwalpulkit596]

LGTM @anandwana001 do you have anything else or should i go ahead and merge this one.

[anandwana001]

@rt4914 I will defer to Rajat. Please also fill the contributor survey to take contributions further.
Also, checks are failing.

[rt4914]

LGTM, thanks. @anandwana001 You can make a note of this as you are the onboarding mentor.

[anandwana001]

@rt4914 Thanks