hush: fix readonly2.tests failure

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

shell/hush.c

@@ -2287,7 +2287,18 @@ static struct variable *set_vars_and_save_old(char **strings)
 			if (var_pp) {
 				var_p = *var_pp;
 				if (var_p->flg_read_only) {
+					char **p;
 					bb_error_msg("%s: readonly variable", *s);
+					/*
+					 * "VAR=V BLTIN" unsets VARs after BLTIN completes.
+					 * If VAR is readonly, leaving it in the list
+					 * after asssignment error (msg above)
+					 * causes doubled error message later, on unset.
+					 */
+					debug_printf_env("removing/freeing '%s' element\n", *s);
+					free(*s);
+					p = s;
+					do { *p = p[1]; p++; } while (*p);
 					goto next;
 				}
 				/* Remove variable from global linked list */

shell/hush_test/hush-vars/readonly2.right

@@ -1,4 +1,5 @@
 hush: a=Z: readonly variable
 Visible:42
+
 hush: a=Z: readonly variable
 Visible:42

shell/hush_test/hush-vars/readonly2.tests

@@ -3,4 +3,5 @@ readonly a=A
 
 # external commands and builtins should behave the same:
 (exit 42); a=Z echo "Visible:$?"
+echo
 (exit 42); a=Z env echo "Visible:$?"