MDEV-17095 pam_user_map module throws syntax error if group name contains backslash.

Let '\\' and '/' symbols to be part of a group name.

plugin/auth_pam/mapper/pam_user_map.c

@@ -189,13 +189,15 @@ int pam_sm_authenticate(pam_handle_t *pamh, int flags,
       s++;
     }
     from= s;
-    skip(isalnum(*s) || (*s == '_') || (*s == '.') || (*s == '-') || (*s == '$'));
+    skip(isalnum(*s) || (*s == '_') || (*s == '.') || (*s == '-') ||
+         (*s == '$') || (*s == '\\') || (*s == '/'));
     end_from= s;
     skip(isspace(*s));
     if (end_from == from || *s++ != ':') goto syntax_error;
     skip(isspace(*s));
     to= s;
-    skip(isalnum(*s) || (*s == '_') || (*s == '.') || (*s == '-') || (*s == '$'));
+    skip(isalnum(*s) || (*s == '_') || (*s == '.') || (*s == '-') ||
+         (*s == '$'));
     end_to= s;
     if (end_to == to) goto syntax_error;