avformat/icodec: Check for zero streams and stream creation failure

Fixes: NULL pointer dereference
Fixes: 26814/clusterfuzz-testcase-minimized-ffmpeg_dem_ICO_fuzzer-5758487797432320

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Reviewed-by: Peter Ross <pross@xvid.org>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit b33233bd53)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavformat/icodec.c

@@ -84,6 +84,9 @@ static int read_header(AVFormatContext *s)
     avio_skip(pb, 4);
     ico->nb_images = avio_rl16(pb);
 
+    if (!ico->nb_images)
+        return AVERROR_INVALIDDATA;
+
     ico->images = av_malloc_array(ico->nb_images, sizeof(IcoImage));
     if (!ico->images)
         return AVERROR(ENOMEM);
@@ -93,7 +96,7 @@ static int read_header(AVFormatContext *s)
         int tmp;
 
         if (avio_seek(pb, 6 + i * 16, SEEK_SET) < 0)
-            break;
+            goto fail;
 
         st = avformat_new_stream(s, NULL);
         if (!st) {
@@ -118,7 +121,7 @@ static int read_header(AVFormatContext *s)
         ico->images[i].offset = avio_rl32(pb);
 
         if (avio_seek(pb, ico->images[i].offset, SEEK_SET) < 0)
-            break;
+            goto fail;
 
         codec = avio_rl32(pb);
         switch (codec) {