More style cleanup in GIFImageReader
https://bugs.webkit.org/show_bug.cgi?id=110776

Reviewed by Allan Sandfeld Jensen.

Renamed variable q to currentComponent which more accurately represent
the purpose.

No test. Simple refactoring.

* platform/image-decoders/gif/GIFImageReader.cpp:
(GIFImageReader::decodeInternal):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@144257 268f45cc-cd09-0410-ab3c-d52691b4dbfc