address another warning

sounds.c: In function ‘domonnoise’:
sounds.c:818:40: warning: array subscript [0, 1] is outside array bounds of ‘const char * const[2]’ [-Warray-bounds=]
  818 |                     verbl_msg = vampmsg[vampindex];
      |                                 ~~~~~~~^~~~~~~~~~~
sounds.c:786:38: note: while referencing ‘vampmsg’
  786 |             static const char *const vampmsg[] = {
      |                                      ^~~~~~~

src/sounds.c

@@ -814,8 +814,10 @@ domonnoise(struct monst *mtmp)
                                                flags.female ? FEMALE : MALE))
                                    : an(racenoun));
                     verbl_msg = verbuf;
-                } else
-                    verbl_msg = vampmsg[vampindex];
+                } else if (vampindex > 1) {
+                    if (vampindex >= 0 && vampindex < SIZE(vampmsg))
+                        verbl_msg = vampmsg[vampindex];
+                }
             }
         }
         break;