Fix stderr printing

zstdwarccat

@@ -21,7 +21,7 @@ def get_dict(fp):
 		# Decompress with unzstd
 		p = subprocess.Popen(['unzstd'], stdin = subprocess.PIPE, stdout = subprocess.PIPE, stderr = subprocess.PIPE)
 		out, err = p.communicate(d)
-		assert p.returncode == 0, f'unzstd exited non-zero: return code {p.returncode}, stderr: {p.stderr!r}'
+		assert p.returncode == 0, f'unzstd exited non-zero: return code {p.returncode}, stderr: {err!r}'
 		d = out
 	#elif d.startswith(b'\x37\xA4\x30\xEC'): # Uncompressed dict, nothing to do
 	return d