API:swscale with slices gives bad output

[rxt]

Summary of the bug:
After the fix in #4877 the scaler no longer crashes with slices, but the output is totally wrong. Only some lines at the top of the image are drawn, the rest of the picture is black.
Also this time undefining FILTER_NEW in swscale_internal.h fixes it.

How to reproduce:
Compile and run the attached code

gcc -g scaling_r.c  -L/usr/local/lib -lswscale -lm -lavutil -o scaling_r

It will create a file named "qqq". Play the resulting file with

ffplay -f rawvideo -pix_fmt rgb24 -video_size 720x540 qqq

To see how the picture should look line just recompile and run the code defining NO_SLICES

Version
ffmpeg version N-74836-gaff3acc Copyright (c) 2000-2015 the FFmpeg developers

built with gcc 4.9.2 (Debian 4.9.2-10)
configuration: --enable-gpl --enable-postproc --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-nonfree --enable-version3 --enable-libmp3lame --samples=fate-suite/
libavutil 55. 2.100 / 55. 2.100
libavcodec 57. 3.100 / 57. 3.100
libavformat 57. 2.100 / 57. 2.100
libavdevice 57. 0.100 / 57. 0.100
libavfilter 6. 8.100 / 6. 8.100
libswscale 4. 0.100 / 4. 0.100
libswresample 2. 0.100 / 2. 0.100
libpostproc 54. 0.100 / 54. 0.100

[Carl Eugen Hoyos]

Regression since 62d176de1224f6b9921a53171e5daa7460d5a772

[Pedro Arthur]

Fixed in 5bd62a1b3c3356b84818efca3fcaf52da27a32af