Don't permit C-x 8 RET &c in isearch.el to contaminate search string

Don't permit C-x 8 RET &c in isearch.el to contaminate search string

* lisp/isearch.el (isearch-char-by-name, isearch-emoji-by-name):
Concatenate new character to the query string saved by
with-isearch-suspended, not the current string, which might have
been modified by recursive I-search sessions within
completing-read.

(cherry picked from commit e0993f5169ebf761d520b2e23630a3de7d13ccb3)