tests: core: A few more Blit Clipped tests.

Signed-off-by: Cyril Hrubis <metan@ucw.cz>
core: BlitClipped: Fix two special cases.

* When dest coordinates (x2, y2) are negative
  we need to clip source rectangle and not move it

* Fix off by one bugs when checking that source rectangle
  fits into destination context

Fixes segfaults in spiv when moving image to the
bottom right corner.

Reported-by: Milan Vancura <milan@ucw.cz>
Signed-off-by: Cyril Hrubis <metan@ucw.cz>
loaders: TIFF: Fix warnings.

Fix unused warnings when compiling without the TIFF library.

Signed-off-by: Cyril Hrubis <metan@ucw.cz>