avcodec/tests/rangecoder: initialize array to avoid valgrind warning

Found-by: jamrial
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit c15972f0af)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/tests/rangecoder.c

@@ -29,7 +29,7 @@
 int main(void)
 {
     RangeCoder c;
-    uint8_t b[9 * SIZE];
+    uint8_t b[9 * SIZE] = {0};
     uint8_t r[9 * SIZE];
     int i;
     uint8_t state[10];