Set haveGlyphs=true when the glyph page contains a space glyph.

When a glyph page contains only space glyphs, the page is not
marked as "haveGlyphs" and the page is not used. This sometimes
breaks rendering space by such fonts (e.g., Droid Arabic Kufi.)

The test font SpaceAndHiraganaA.woff is created by me using
FontForge (the existing test font SpaceOnly.otf is copied and
its blank glyph for U+0020 is copied to U+3042).

BUG=268804
R=tkent@chromium.org

Review URL: https://codereview.chromium.org/25603003

git-svn-id: svn://svn.chromium.org/blink/trunk@158775 bbb929c8-8fbe-4397-9dbb-9b2b20218538