Fix thinko in _alpm_strip_newline

The point of this early compare to NULL byte check was so we could bail
early and skip the strcmp() call. Given we weren't doing the check
right, this never exited early. Fix it to work as intended.

Noticed-by: Pepe Juárez <trulustapa@gmail.com>
Signed-off-by: Dan McGee <dan@archlinux.org>

lib/libalpm/util.c

@@ -221,7 +221,7 @@ char *_alpm_strtrim(char *str)
 size_t _alpm_strip_newline(char *str)
 {
 	size_t len;
-	if(str == '\0') {
+	if(*str == '\0') {
 		return 0;
 	}
 	len = strlen(str);