ffprobe: only hash extradata when it is present

Passing zero-sized/NULL buffers to av_hash_update() is invalid and may
crash with certain hashes.

fftools/ffprobe.c

@@ -2748,8 +2748,11 @@ static int show_stream(WriterContext *w, AVFormatContext *fmt_ctx, int stream_id
     if (do_show_data)
         writer_print_data(w, "extradata", par->extradata,
                                           par->extradata_size);
-    writer_print_data_hash(w, "extradata_hash", par->extradata,
-                                                par->extradata_size);
+
+    if (par->extradata_size > 0) {
+        writer_print_data_hash(w, "extradata_hash", par->extradata,
+                                                    par->extradata_size);
+    }
 
     /* Print disposition information */
 #define PRINT_DISPOSITION(flagname, name) do {                                \

tests/ref/fate/hapqa-extract-nosnappy-to-hapalphaonly-mov

@@ -50,7 +50,6 @@ bits_per_raw_sample=N/A
 nb_frames=1
 nb_read_frames=N/A
 nb_read_packets=1
-extradata_hash=adler32:00000001
 DISPOSITION:default=1
 DISPOSITION:dub=0
 DISPOSITION:original=0

tests/ref/fate/hapqa-extract-nosnappy-to-hapq-mov

@@ -50,7 +50,6 @@ bits_per_raw_sample=N/A
 nb_frames=1
 nb_read_frames=N/A
 nb_read_packets=1
-extradata_hash=adler32:00000001
 DISPOSITION:default=1
 DISPOSITION:dub=0
 DISPOSITION:original=0