cli_readline: Only insert printable chars

There should be no need to insert non-printable characters
and this prevents line editing getting confused.
Signed-off-by: NSteve Bennett <steveb@workware.net.au>

common/cli_readline.c

@@ -493,8 +493,10 @@ static int cread_line(const char *const prompt, char *buf, unsigned int *len,
 		}
 #endif
 		default:
-			cread_add_char(ichar, insert, &num, &eol_num, buf,
-				       *len);
+			if (ichar >= ' ' && ichar <= '~') {
+				cread_add_char(ichar, insert, &num, &eol_num,
+					       buf, *len);
+			}
 			break;
 		}
 	}