golomb: Add a get_se_golomb_long

Useful in libavformat mostly.

(cherry picked from commit 5eacbb5328)

libavcodec/golomb.h

@@ -206,6 +206,18 @@ static inline int get_se_golomb(GetBitContext *gb)
     }
 }
 
+static inline int get_se_golomb_long(GetBitContext *gb)
+{
+    unsigned int buf = get_ue_golomb_long(gb);
+
+    if (buf & 1)
+        buf = -(buf >> 1);
+    else
+        buf = (buf >> 1);
+
+    return buf;
+}
+
 static inline int svq3_get_se_golomb(GetBitContext *gb)
 {
     unsigned int buf;