SVGFontFaceElement::removedFrom should not use FontSelector when document is not active.

BUG=348401
TEST=fast/css/use-incorrect-svg-crash.html
TBR=morrita@chromium.org, dglazkov@chromium.org

Review URL: https://codereview.chromium.org/183743012

git-svn-id: svn://svn.chromium.org/blink/trunk@168271 bbb929c8-8fbe-4397-9dbb-9b2b20218538