Allow FPDFBookmark_GetFirstChild to return the top level bookmark

Previously when passing a NULL bookmark to FPDFBookmark_GetFirstChild it returned NULL instead of returning the top level bookmark. This change removes the early exit in this case allowing the top level bookmark to be retrieved.

BUG=https://code.google.com/p/pdfium/issues/detail?id=110
R=bo_xu@foxitsoftware.com, tsepez@chromium.org

Review URL: https://codereview.chromium.org/847243005
1 file changed