ash: fix ${unset_var/pattern/repl}

function                                             old     new   delta
subevalvar                                          1349    1353      +4

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

shell/ash.c

@@ -7015,7 +7015,8 @@ subevalvar(char *start, char *str, int strloc,
 	slash_pos = -1;
 	if (repl) {
 		slash_pos = expdest - ((char *)stackblock() + strloc);
-		STPUTC('/', expdest);
+		if (!(flag & EXP_DISCARD))
+			STPUTC('/', expdest);
 		//bb_error_msg("repl+1:'%s'", repl + 1);
 		p = argstr(repl + 1, (flag & EXP_DISCARD) | EXP_TILDE); /* EXP_TILDE: echo "${v/x/~}" expands ~ ! */
 		*repl = '/';

shell/ash_test/ash-vars/var_bash_repl_empty_var.right

@@ -1,2 +1,3 @@
 
+
 Ok:0

shell/ash_test/ash-vars/var_bash_repl_empty_var.tests

@@ -1,3 +1,5 @@
+unset v
+echo ${v/*/w}
 v=''
 echo ${v/*/w}
 echo Ok:$?