fix issue #539

[wzy1935]

Description

Fixes the bug that after compression pdf becomes larger. Now the compressed file is always smaller than the original one, and the setting for the compression rate is more effective. No dependency changed.

Fixes #539

Type of change

• [x] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)

How Has This Been Tested?

Test compressing pdf with following three:

book_sample.pdf pdf_with_big_pic.pdf pdf_with_pic_hard_to_compress.pdf

• [x] ./gradlew assembleDebug assembleRelease
• [x] ./gradlew checkstyle

Checklist:

• [x] My code follows the style guidelines of this project
• [x] I have performed a self-review of my own code
• [x] I have commented my code, particularly in hard-to-understand areas
• [x] I have made corresponding changes to the documentation
• [x] My changes generate no new warnings

[codeclimate[bot]]

Code Climate has analyzed commit 010e62e7 and detected 2 issues on this pull request.

Here's the issue category breakdown:

Category	Count
Complexity	2

View more on Code Climate.

[wzy1935]

@codegsaini Hi! I refactored it in bf63f0e. I think it can pass complexity analysis now?

[wzy1935]

@codegsaini It should work now. Thank you for the code review!