bug#22327: 25.1.50; navigating to image in eww in a term (shr-put-image)

[Mark Oteiza]

Navigating to an image (lacking alt text) in a non-graphic emacs errors
in shr-put-image, because (insert nil) is an error.

Doing eww-open-file on a local image file should be sufficient to
reproduce.

Alternatively, here is a link to a picture of a kitten.
https://upload.wikimedia.org/wikipedia/commons/0/06/Kitten_in_Rizal_Park,_Manila.jpg

In GNU Emacs 25.1.50.1 (x86_64-unknown-linux-gnu, X toolkit, Xaw scroll bars)
 of 2016-01-05 built on ethos
Repository revision: 6a311d2072b8a4ea530d9a541e661a8ad11bb1d7
Configured using:
 'configure --prefix=/usr --sysconfdir=/etc --libexecdir=/usr/lib
 --localstatedir=/var --without-gconf --with-modules
 --with-x-toolkit=lucid 'CFLAGS=-march=x86-64 -mtune=sandybridge -O3
 -pipe -fstack-protector-strong --param=ssp-buffer-size=4'
 CPPFLAGS=-D_FORTIFY_SOURCE=2
 LDFLAGS=-Wl,-O1,--sort-common,--as-needed,-z,relro'

Configured features:
XPM JPEG TIFF GIF PNG RSVG IMAGEMAGICK SOUND GPM DBUS GSETTINGS NOTIFY
ACL GNUTLS LIBXML2 FREETYPE M17N_FLT LIBOTF XFT ZLIB TOOLKIT_SCROLL_BARS
LUCID X11 MODULES