remove invalid skip of locking in ungetwc

aside from being invalid, the early check only optimized the error
case, and likely pessimized the common case by separating the
two branches on isascii(c) at opposite ends of the function.
diff --git a/src/stdio/ungetwc.c b/src/stdio/ungetwc.c
index 913f716..0a4cd7a 100644
--- a/src/stdio/ungetwc.c
+++ b/src/stdio/ungetwc.c
@@ -11,18 +11,15 @@
 
 	if (c == WEOF) return c;
 
-	/* Try conversion early so we can fail without locking if invalid */
-	if (!isascii(c) && (l = wctomb((void *)mbc, c)) < 0)
-		return WEOF;
-
 	FLOCK(f);
 
 	f->mode |= f->mode+1;
 
 	if (!f->rpos) __toread(f);
-	if (!f->rpos || f->rpos < f->buf - UNGET + l) {
+	if (!f->rpos || f->rpos < f->buf - UNGET + l ||
+	    (!isascii(c) && (l = wctomb((void *)mbc, c)) < 0)) {
 		FUNLOCK(f);
-		return EOF;
+		return WEOF;
 	}
 
 	if (isascii(c)) *--f->rpos = c;