Apply upstream commit 33312fd828e59c78ae4ee30fd70d0ca109748cf0 (by

zoulasc) to contrib/file:

  don't write a char to a pointer.

MFC after:	3 days

contrib/file/compress.c

@@ -480,7 +480,7 @@ uncompressbuf(struct magic_set *ms, int fd, size_t method,
 #endif
 			free(*newch);
 			n = 0;
-			newch[0] = '\0';
+			*newch = NULL;
 			goto err;
 		} else {
 			n = r;