android: only do gradle afterEvaluate when building this lib alone

[zxcpoiu]

Motivation

The afterEvaluate section in build.gradle breaks the RN building from source. ( I'm testing RN 0.67 )
Throws:

* What went wrong:
A problem occurred configuring project ':react-native-blob-util'.
> Could not resolve all files for configuration ':react-native-blob-util:debugCompileClasspath'.
   > Could not resolve com.facebook.react:react-native:+.
     Required by:
         project :react-native-blob-util
      > No matching configuration of project :ReactAndroid was found. The consumer was configured to find an API of a component, as well as attribute 'com.android.build.api.attributes.BuildTypeAttr' with value 'debug' but:
          - None of the consumable configurations have attributes.

Seems the afterEvaluate in build.gradle is only needed when build/publish this lib alone, this PR add a check to ignore the process when building the RN app (via early return) to prevent unnecessary polluting variable and cause main RN app build failed.

Test Plan

• This lib's ./gradlew build and ./gradlew publish should work like in Fix Gradle 7 deprecations #68
• RN App should build successfully

maybe related: #72

[zxcpoiu]

@kklopfenstein sorry for bothering, is this PR make sense to you? I'm not quite sure what it does in detail in afterEvaluated