utils: do not write to 0 sized buffer

src/lxc/utils.c

@@ -2330,9 +2330,11 @@ int run_command(char *buf, size_t buf_size, int (*child_fn)(void *), void *args)
 	/* close the write-end of the pipe */
 	close(pipefd[1]);
 
-	bytes = read(pipefd[0], buf, (buf_size > 0) ? (buf_size - 1) : 0);
-	if (bytes > 0)
-		buf[bytes - 1] = '\0';
+	if (buf && buf_size > 0) {
+		bytes = read(pipefd[0], buf, buf_size - 1);
+		if (bytes > 0)
+			buf[bytes - 1] = '\0';
+	}
 
 	fret = wait_for_pid(child);
 	/* close the read-end of the pipe */