ed(1): Cleanups for the DES mode.

- Use arc4random_uniform(3).
- Prevent a segmentation fault when ed receives a signal
  while being in getpass(). [1]

Obtained from:	OpenBSD [1] (CVS Rev. 1.15)
MFC after:	2 weeks

bin/ed/cbc.c

@@ -99,7 +99,7 @@ init_des_cipher(void)
 
 	/* initialize the padding vector */
 	for (i = 0; i < 8; i++)
-		pvec[i] = (char) (arc4random() % 256);
+		pvec[i] = (char)arc4random_uniform(256);
 #endif
 }
 
@@ -164,7 +164,7 @@ get_keyword(void)
 	/*
 	 * get the key
 	 */
-	if (*(p = getpass("Enter key: "))) {
+	if ((p = getpass("Enter key: ")) != NULL && *p != '\0') {
 
 		/*
 		 * copy it, nul-padded, into the key area