seq could be set on small random images

images under the disc threshold opened in random access mode from
sequential loaders would have the seq tag set on them, causing
performance problems with vips_resize()

see https://github.com/jcupitt/libvips/issues/840

ChangeLog

@@ -6,6 +6,7 @@
 - bump wrapper script version [bgilbert]
 - fix a memleak on error during jpeg buffer write [lovell]
 - fix misspelling of IPTC as IPCT [lovell]
+- seq could be set on small images opened in random-access mode [aferrero2707]
 
 15/4/17 started 8.6.0
 - supports fits images with leading non-image HDUs, thanks benepo

libvips/foreign/foreign.c

@@ -838,7 +838,6 @@ vips_foreign_load_start( VipsImage *out, void *a, void *b )
 		 */
 		vips_image_pipelinev( load->out, load->out->dhint, 
 			load->real, NULL );
-
 	}
 
 	return( vips_region_new( load->real ) );
@@ -951,6 +950,14 @@ vips_foreign_load_build( VipsObject *object )
 			vips_stop_one, 
 			NULL, load ) ) 
 			return( -1 );
+
+		/* We have delayed load. This must mean that the loader will
+		 * load to a memory buffer or temp file, and will therefore
+		 * support random access. 
+		 *
+		 * Make sure there's no seq flag set on the output image. 
+		 */
+		(void) vips_image_remove( load->out, VIPS_META_SEQUENTIAL );
 	}
 
 	return( 0 );

libvips/iofuncs/image.c

@@ -3139,7 +3139,8 @@ vips_image_copy_memory( VipsImage *image )
  * image might have been shared, use the less efficient
  * vips_image_copy_memory() instead.
  *
- * See also: vips_image_copy_memory(), vips_image_pio_input(), vips_image_inplace(), VIPS_IMAGE_ADDR().
+ * See also: vips_image_copy_memory(), vips_image_pio_input(), 
+ * vips_image_inplace(), VIPS_IMAGE_ADDR().
  *
  * Returns: 0 on succeess, or -1 on error.
  */