bug#21870: 25.0.50; image now shown after decrypting image file

[Dirk-Jan C . Binnema]

It seems the auto-decryption functionality does not work correctly for
encrypted images - that is, decryption works, but then the image is not
shown.

Steps to reproduce:
1) Open an encrypted image file (say, test.jpeg.gpg)
2) Enter the passphrase, when asked (by easypg I assume)
3) Now, see a small rectangle in the upper left of the current window;
   instead of the expected image

Expected behavior would be to see the image, just as if opening
test.jpeg directly.

The mentioned rectangle does seem to point the correct data (when
looking at it with image-toggle-display. 

In GNU Emacs 25.0.50.129 (x86_64-unknown-linux-gnu, GTK+ Version 3.18.2)
 of 2015-11-02
Repository revision: d4352f813a0703cc7f7a873525131b272ef0c105
Windowing system distributor 'Fedora Project', version 11.0.11799902
System Description:     Fedora release 23 (Twenty Three)

Configured using:
 'configure
 
PKG_CONFIG_PATH=/usr/local/lib/pkgconfig:/usr/local/share/pkgconfig:/usr/lib/pkgconfig::/usr/local/Cellar/sqlite/3.7.15.1/lib/pkgconfig/'

Configured features:
XPM JPEG TIFF GIF PNG IMAGEMAGICK SOUND DBUS GSETTINGS NOTIFY ACL
LIBSELINUX GNUTLS LIBXML2 FREETYPE XFT ZLIB TOOLKIT_SCROLL_BARS GTK3 X11