avcodec/jpeg2000htdec: Avoid freeing uninitialized pointers in ff_jpeg2000_decode_htj2k()

Fixes: freeing of uninitialized pointers
Fixes: part of 58299

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Reviewed-by: Tomas Härdin <git@haerdin.se>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/jpeg2000htdec.c

@@ -1174,8 +1174,8 @@ ff_jpeg2000_decode_htj2k(const Jpeg2000DecoderContext *s, Jpeg2000CodingStyle *c
     int ret;
 
     /* Temporary buffers */
-    int32_t *sample_buf;
-    uint8_t *block_states;
+    int32_t *sample_buf = NULL;
+    uint8_t *block_states = NULL;
 
     int32_t n, val;             // Post-processing