tweaks: remove two redundant conditions, and make a more direct return

The escape-parsing routine nowadays returns FOREIGN_SEQUENCE instead
of ERR when encountering an unknown sequence.  So, with the two cases
that demand ERR now handled directly, there is no need to check for
ERR any more.

src/winio.c

@@ -1026,11 +1026,11 @@ int parse_kbinput(WINDOW *win)
 					}
 					escapes = 0;
 				}
-			} else if (keycode == '[' && key_buffer_len > 0 &&
-						(('A' <= *key_buffer && *key_buffer <= 'D') ||
-						('a' <= *key_buffer && *key_buffer <= 'd'))) {
+			} else if (keycode == '[' && (('A' <= *key_buffer && *key_buffer <= 'D') ||
+										('a' <= *key_buffer && *key_buffer <= 'd'))) {
 				/* An iTerm2/Eterm/rxvt sequence: ^[ ^[ [ X. */
 				double_esc = TRUE;
+				return ERR;
 			} else {
 				/* Two escapes followed by a non-escape, and there are more
 				 * codes waiting: combined meta and escape sequence mode. */
@@ -1058,9 +1058,6 @@ int parse_kbinput(WINDOW *win)
 			break;
 	}
 
-	if (retval == ERR)
-		return ERR;
-
 	if (retval == controlleft)
 		return CONTROL_LEFT;
 	else if (retval == controlright)