[Pkg-gmagick-im-team] Bug#845198: Check validity of extend during TIFF file reading

[Bastien ROUCARIES]

Package: src:imagemagick
version: 8:6.8.9.9-5+deb8u5
Severity: important
Tags: patch security
X-Debbugs-CC: secure-testing-team at lists.alioth.debian.org
control: found -1 8:6.7.7.10-5+deb7u7

    This will avoid a buffer overflow

Found during git tree review

    origin; https://github.com/ImageMagick/ImageMagick/commit/2bb6941a2d557f26a2f2049ade466e118eeaab91