Fix logic used to build fuzzy search regex

The intent was to insert '*' between all characters in the query, except
for those which were escaped with '\'. What the old implementation did,
however, was strip out all backslashes and place '*' between all
remaining characters, as when a backslash was detected the loop would
skip to the next character without appending the backslash to the regex.

The new logic is something like "add the character, then add '*' if the
character was not a backslash", which should be correct

zsh-history-substring-search.zsh

@@ -220,8 +220,8 @@ _history-substring-search-begin() {
 
     fuzzy_regex="*"
     for char ({1..$#escaped_query}); do
-      [[ escaped_query[$char] == '\' ]] && continue
-      fuzzy_regex+="${escaped_query[$char]}*"
+      fuzzy_regex+="${escaped_query[$char]}"
+      [[ escaped_query[$char] != '\' ]] && fuzzy_regex+="*"
     done
 
     #