tiffenc: fix out of array read

Fixes ticket1112

Found-by: ami_stuff
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/tiffenc.c

@@ -193,13 +193,24 @@ static void pack_yuv(TiffEncoderContext * s, uint8_t * dst, int lnum)
     int w = (s->width - 1) / s->subsampling[0] + 1;
     uint8_t *pu = &p->data[1][lnum / s->subsampling[1] * p->linesize[1]];
     uint8_t *pv = &p->data[2][lnum / s->subsampling[1] * p->linesize[2]];
-    for (i = 0; i < w; i++){
-        for (j = 0; j < s->subsampling[1]; j++)
-            for (k = 0; k < s->subsampling[0]; k++)
-                *dst++ = p->data[0][(lnum + j) * p->linesize[0] +
-                                    i * s->subsampling[0] + k];
-        *dst++ = *pu++;
-        *dst++ = *pv++;
+    if(s->width % s->subsampling[0] || s->height % s->subsampling[1]){
+        for (i = 0; i < w; i++){
+            for (j = 0; j < s->subsampling[1]; j++)
+                for (k = 0; k < s->subsampling[0]; k++)
+                    *dst++ = p->data[0][FFMIN(lnum + j, s->height-1) * p->linesize[0] +
+                                        FFMIN(i * s->subsampling[0] + k, s->width-1)];
+            *dst++ = *pu++;
+            *dst++ = *pv++;
+        }
+    }else{
+        for (i = 0; i < w; i++){
+            for (j = 0; j < s->subsampling[1]; j++)
+                for (k = 0; k < s->subsampling[0]; k++)
+                    *dst++ = p->data[0][(lnum + j) * p->linesize[0] +
+                                        i * s->subsampling[0] + k];
+            *dst++ = *pu++;
+            *dst++ = *pv++;
+        }
     }
 }