geeqie crashes on non-image suffix

Geeqie crashes, if you open a file with no or non-image suffix.

steps to reproduce:
* copy an image file to a name without image suffix, e.g. cp image.png /tmp/image.nonimagesuffix
* call geeqie on it: geeqie /tmp/image.nonimagesuffix
* crash with message on console: ERROR:filedata.c:1101:file_data_new_group: assertion failed: (fd)

for your convenience I have created a script to demonstrate the issue.
It creates a png image file with wrong suffix (via imagemagick) and links it to two names with the suffixes png and jpg.
Calling geeqie on these files that geeqie crashes on file with wrong suffix, and is fine with the link names (.png/.jpg).
If the suffix (jpg) does not match the content type (png), but is an image suffix, there is no problem.

Expected behaviour:
* geeqie should not crash and find out, what kind of image data there is in the file.

ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: geeqie 1:1.1-8
ProcVersionSignature: Ubuntu 3.13.0-32.57-generic 3.13.11.4
Uname: Linux 3.13.0-32-generic x86_64
NonfreeKernelModules: openafs
ApportVersion: 2.14.1-0ubuntu3.2
Architecture: amd64
CurrentDesktop: Unity
Date: Thu Jul 31 09:56:51 2014
EcryptfsInUse: Yes
InstallationDate: Installed on 2014-01-14 (197 days ago)
InstallationMedia: Ubuntu 13.10 "Saucy Salamander" - Release amd64 (20131016.1)
SourcePackage: geeqie
UpgradeStatus: Upgraded to trusty on 2014-07-06 (24 days ago)