Free the GifPlainText object when complete.
Free the GifPlainText object when complete.

We allocate the GifPlainText object on line ~685 inside GIF_D_STATUS_EXT_PTE.
We cleanup the internal pointers in the gif_destroy_decompress() but we
failed to cleanup the pointer itself.

This CL frees the allocated pointer once the data is cleaned up.

BUG=chromium:638499

Review-Url: https://codereview.chromium.org/2291143003

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