Add CVE-2018-1000100/gpac

gpac is not affected by the buffer overflow flaw in
src/isomedia/avc_ext.c , which is associated with CVE-2018-1000100 .
Interestingly the fixing commit for

https://github.com/gpac/gpac/issues/994

which is

https://github.com/gpac/gpac/commit/90dc7f853d31b0a4e9441cba97feccf36d8b69a4

adresses as well another buffer overflow flaw in
src/media_tools/av_parsers.c wich is not covere by the CVE description.
The second one is

https://github.com/gpac/gpac/issues/997

Asked MITRE for clarification if another CVE has to be assigned or we
can cover both issues with this CVE.