[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'.

ChangeLog

@@ -1,3 +1,18 @@
+2015-01-14  Behdad Esfahbod  <behdad@behdad.org>
+
+	[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'.
+
 2015-01-14  Behdad Esfahbod  <behdad@behdad.org>
 
 	[base] Don't initialize unused `driver->glyph_loader'.

src/smooth/ftgrays.c

@@ -1985,6 +1985,7 @@ typedef ptrdiff_t  FT_PtrDist;
     ras.invalid        = 1;
     ras.band_size      = band_size;
     ras.num_gray_spans = 0;
+    ras.span_y         = 0;
 
     if ( params->flags & FT_RASTER_FLAG_DIRECT )
     {