Fix regression in option parsing

Commit ec229bbe7 broke invocation without a specific -hda.  IOW, qemu foo.img.
The lack of an optind update caused an infinite loop.

Reported-by: Amit Shah <amit.shah@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
diff --git a/vl.c b/vl.c
index 1cd355c..6f1e1ab 100644
--- a/vl.c
+++ b/vl.c
@@ -4819,6 +4819,7 @@
     while (optind < argc) {
         if (argv[optind][0] != '-') {
             /* disk image */
+            optind++;
             continue;
         } else {
             const QEMUOption *popt;