imlib2: multiple issues

• CVE-2011-5326 (denial of service)

Kevin Ryde discovered that attempting to draw a 2x1 radi ellipse results
in a floating point exception.

• CVE-2016-3993 (information leakage)

Yuriy M. Kaminskiy discovered that drawing using coordinates from an
untrusted source could lead to an out-of-bound memory read, which in
turn could result in an application crash.

• CVE-2016-3994 (information Leakage)

Jakub Wilk discovered that a malformed image could lead to an
out-of-bound read in the GIF loader, which may result in an application
crash or information leak.

• CVE-2016-4024 (arbitrary code execution)

Yuriy M. Kaminskiy discovered an integer overflow that could lead to an
insufficient heap allocation and out-of-bound memory write.