Progressive JPEG outputScanlines() calls should handle failure

outputScanlines() can fail and delete |this|, so any attempt to access
members thereafter should be avoided. Copy the decoder pointer member,
and use that copy to detect and handle the failure case.

BUG=232763
R=pkasting@chromium.org

Review URL: https://codereview.chromium.org/14844003

git-svn-id: svn://svn.chromium.org/blink/trunk@150545 bbb929c8-8fbe-4397-9dbb-9b2b20218538
inline bool colorSpaceHasAlpha(J_COLOR_SPACE colorSpace) { return turboSwizzled(colorSpace); }

inline bool colorSpaceHasAlpha(J_COLOR_SPACE colorSpace) { return turboSwizzled(colorSpace); }
