[smooth] Fix uninitialized memory access.

Looks like `ras.span_y' could always be used without initialization.
This was never detected by valgrind before because the library-wide
`raster_pool' was used for the worker object and `raster_pool' was
originally zero'ed.  But subsequent reuses of it were using `span_y'
uninitialized.  With the recent change to not use `render_pool' and
allocate worker and buffer on the stack, valgrind now detects this
uninitialized access.

* src/smooth/ftgrays.c (gray_raster_render): Initialize
`ras.span_y'.
2 files changed