migration: don't use uninitialized variables

The qmp_migrate method uses the 'blk' and 'inc' parameter without
checking if they're valid or not (they may be uninitialized if
command is received via QMP)

Signed-off-by: Pawit Pornkitprasan <p.pawit@gmail.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>

migration.c

@@ -400,8 +400,8 @@ void qmp_migrate(const char *uri, bool has_blk, bool blk,
     MigrationParams params;
     const char *p;
 
-    params.blk = blk;
-    params.shared = inc;
+    params.blk = has_blk && blk;
+    params.shared = has_inc && inc;
 
     if (s->state == MIG_STATE_ACTIVE || s->state == MIG_STATE_SETUP) {
         error_set(errp, QERR_MIGRATION_ACTIVE);