vi - inability to search backwards for ?

[Jeremy Mates]

A search for /\/ is okay; this discards the \ and searches for "/"

A search for ?\? is not okay; this discards the \ and searches for "?"
which is an invalid regular expression, "RE error: repetition-operator
operand invalid".

A problematic bare leading ? on a backwards search can be escaped by
the following, though I'm not sure if that's an ideal fix. Thoughts?

--- search.c.orig       Sat Dec 10 08:06:18 2022
+++ search.c    Fri May 12 23:05:31 2023
@@ -120,6 +120,12 @@
                plen = t - ptrn;
        }
 
+       if (delim == '?' && *ptrn == '?') {
+               ptrn--;
+               plen++;
+               *ptrn = '\\';
+       }
+
        /* Compile the RE. */
        if (re_compile(sp, ptrn, plen, &sp->re, &sp->re_len, &sp->re_c,
            RE_C_SEARCH |