[9front] cmd/acme: fix user after free in wind.c (patch)

[boehm.igor@gmail.com]

The function /sys/src/cmd/acme/wind.c:/^winaddincl contains a use
after free.

Below is a possible patch that also hopefully demonstrates the issue
where 'a' is freed but might be used later to format a warning:

diff -r 0b8c8ef6a3d4 sys/src/cmd/acme/wind.c
--- a/sys/src/cmd/acme/wind.c	Tue Jan 19 15:18:57 2021 -0800
+++ b/sys/src/cmd/acme/wind.c	Tue Feb 02 01:55:54 2021 +0100
@@ -610,13 +610,14 @@
 		r = runerealloc(r, n+1);
 		r[n] = 0;
 	}
-	free(a);
 	if((d->qid.type&QTDIR) == 0){
 		free(d);
 		warning(nil, "%s: not a directory\n", a);
 		free(r);
+		free(a);
 		return;
 	}
+	free(a);
 	free(d);
 	w->nincl++;
 	w->incl = realloc(w->incl, w->nincl*sizeof(Rune*));