isl_input.c: vars_drop: fix error handling

diff --git a/isl_input.c b/isl_input.c
index 8747e56..493e7ac 100644 (file)
--- a/isl_input.c
+++ b/isl_input.c
@@ -68,7 +68,7 @@ static void vars_drop(struct vars *v, int n)
 {
        struct variable *var;
 
-       if (!v)
+       if (!v || !v->v)
                return;
 
        v->n -= n;