[librsvg] (9 commits) ...Merge branch 'bbox-checks' into 'master'

[Federico Mena Quintero <federico src gnome org>]

Summary of changes:

  d6dc59d... BoundingBox: new functions rect_is_empty / ink_rect_is_empt
  dd48a2e... generate_cairo_mask: Don't push the mask_cr for longer than
  d77abc9... generate_cairo_mask - Create the bounding box transform as 
  31342b3... Rename Transform::new to new_unchecked
  de76d1b... DrawingCtx::clip_to_node - Prepare for switching to Boundin
  89f21a7... clip_to_node - Use a new function BoundingBox.rect_to_trans
  5041fc3... gradient: use bbox.rect_to_transform instead of checking th
  a869370... (#593): Don't panic with an empty objectBoundingBox for a m
  d7e33b2... Merge branch 'bbox-checks' into 'master'