compress: limit the output to dst_max bytes with LZ4 if set

We already do that with other algorithms, so let's make
decompress_blob_lz4() consistent with the rest.

src/basic/compress.c

@@ -739,6 +739,8 @@ static int decompress_blob_lz4(
         size = unaligned_read_le64(src);
         if (size < 0 || (unsigned) size != unaligned_read_le64(src))
                 return -EFBIG;
+        if (dst_max > 0 && (size_t) size > dst_max)
+                return -ENOBUFS;
         out = greedy_realloc(dst, size, 1);
         if (!out)
                 return -ENOMEM;