Fix a memory leak in CPDF_SecurityHandler.
Fix a memory leak in CPDF_SecurityHandler.

AES256_CheckPassword() leaks memory on failure.
Clean up some nits.

BUG=chromium:659468

Review-Url: https://codereview.chromium.org/2463183002

DrAlexx/pdfium,DrAlexx/pdfium,DrAlexx/pdfium,DrAlexx/pdfium