more zero-length changes for svg compatibility

more zero-length changes for svg compatibility

If a path contains a moveTo followed by a line or curve,
even if the line or curve has no length, SVG expects
the end caps to draw if the cap style is round or square.

Fredrik Söderquist attached a patch to the chrome bug
(slightly modified here) that fixes layout test failures
resulting from deleting special-case code in SVG
dealing with zero-length path segments.

R=reed@google.com,fs@opera.com
BUG=22974

Review URL: https://codereview.chromium.org/1330623003