Use size_t to store buffer sizes. With this (and probably following), DT can open 26770x13385 TIFF
_read_planar_16(): get rid of dt_imageio_write_pos()
Was done when trying to open 26770x13385 TIFF
_read_planar_f(): get rid of dt_imageio_write_pos()
_read_planar_8(): get rid of dt_imageio_write_pos()
TIFF ImageIO: cleanup: remove unused orientation from struct tiff_t
TIFFReadScanline() can fail. report it back to dt_imageio_open_tiff()
TIFF ImageIO: replace imagelength with height and drop imagelength
TIFF ImageIO: alloc only 1 buf.
This also fixes potential issues when buf was not allocated or if(t.spp > 1 && config != PLANARCONFIG_CONTIG)
Merge pull request #670 from LebedevRI/tiff-358mpix

Fix opening 358MPix Tiff