huffyuvdec: Skip len==0 cases

Fixes vlc decoding for hypothetical files that would contain such cases.

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
(cherry picked from commit 0dfc01c2bb)

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
(cherry picked from commit 5ff41ffeb4)

Conflicts:

	libavcodec/huffyuv.c
(cherry picked from commit 9bc70fe1ae)

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

libavcodec/huffyuv.c

@@ -312,11 +312,11 @@ static void generate_joint_tables(HYuvContext *s){
             for(i=y=0; y<256; y++){
                 int len0 = s->len[0][y];
                 int limit = VLC_BITS - len0;
-                if(limit <= 0)
+                if(limit <= 0 || !len0)
                     continue;
                 for(u=0; u<256; u++){
                     int len1 = s->len[p][u];
-                    if(len1 > limit)
+                    if (len1 > limit || !len1)
                         continue;
                     assert(i < (1 << VLC_BITS));
                     len[i] = len0 + len1;
@@ -340,17 +340,17 @@ static void generate_joint_tables(HYuvContext *s){
         for(i=0, g=-16; g<16; g++){
             int len0 = s->len[p0][g&255];
             int limit0 = VLC_BITS - len0;
-            if(limit0 < 2)
+            if (limit0 < 2 || !len0)
                 continue;
             for(b=-16; b<16; b++){
                 int len1 = s->len[p1][b&255];
                 int limit1 = limit0 - len1;
-                if(limit1 < 1)
+                if (limit1 < 1 || !len1)
                     continue;
                 code = (s->bits[p0][g&255] << len1) + s->bits[p1][b&255];
                 for(r=-16; r<16; r++){
                     int len2 = s->len[2][r&255];
-                    if(len2 > limit1)
+                    if (len2 > limit1 || !len2)
                         continue;
                     assert(i < (1 << VLC_BITS));
                     len[i] = len0 + len1 + len2;