util: close excessive file descriptors in iobuf_recv_from_fd

Unceremoneously close any fds that the client gives us that exceed our
expectations (which right now is a max of 32 for a protocol-valid max
of... 1).

Assisted-by: Claude:claude-opus-4-6
Part-of: <https://gitlab.freedesktop.org/libinput/libei/-/merge_requests/388>

src/util-io.c

@@ -390,6 +390,12 @@ iobuf_recv_from_fd(struct iobuf *buf, int fd)
 					fd++;
 				}
 			}
+			/* Close any remaining fds that didn't fit in the buffer
+			 * to prevent fd leaks */
+			while (*fd != -1) {
+				xclose(*fd);
+				fd++;
+			}
 		}
 
 		nread += rc;