Fix bug: when uploading a pdf to content page.

[j-nakashima]

To fix a bug that occurs in the following cases.

1. Upoad a single page pdf.
   -> [filename].pdf is created.

2. Upload a multi pages pdf to update.
   -> [filename]_p1.pdf, [filename]_p2.pdf , ... are created.
   but [filename].pdf that can't be read is left.

[kyoshizaki]

Thanks for your commit.
Now I have merged it to master branch.

[kyoshizaki]

To fix a bug that occurs in the following cases.

Upload a single page pdf as PageFile.
-> [filename].pdf is created.

Upload a multi pages pdf as AssetFile to update PageFile.
-> error

[kyoshizaki]

Done!