avcodec: add emuedge_linesize_type

Currently all uses of the emu edge code as well as the code itself
assume int linesize
changing some but not changing all would introduce a security issue
once all use this typedef a simple search and replace can be
done to switch them all to ptrdiff_t

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
(cherry picked from commit 2ffead98dd)

Conflicts:

	libavcodec/videodsp.h

Merged-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/x86/videodsp_init.c

@@ -44,7 +44,7 @@ static av_always_inline void emulated_edge_mc(uint8_t *buf, const uint8_t *src,
                                               emu_edge_core_func *core_fn)
 {
     int start_y, start_x, end_y, end_x, src_y_add = 0;
-    int linesize = linesize_arg;
+    emuedge_linesize_type linesize = linesize_arg;
 
     if(!w || !h)
         return;