[gdk-pixbuf] tests: added a test case for bug 776694

[Bastien Nocera <hadess src gnome org>]

commit 3e625d35f97276c98c8cb3c60cb9b834cf884667
Author: Tobias Mueller <muelli cryptobitch de>
Date:   Sun Jan 1 23:37:05 2017 +0100

    tests: added a test case for bug 776694
    
    afl created a file which ASan complains about:
    io-bmp.c:475:63: runtime error: signed integer overflow: 524672 * 4096 cannot be represented in type 'int'

 tests/test-images/fail/bug776694.bmp |  Bin 0 -> 5089 bytes
 1 files changed, 0 insertions(+), 0 deletions(-)
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diff --git a/tests/test-images/fail/bug776694.bmp b/tests/test-images/fail/bug776694.bmp
new file mode 100644
index 0000000..025eec3
Binary files /dev/null and b/tests/test-images/fail/bug776694.bmp differ