make sure we have regression measurements

src/core/perfmodel/regression.c

@@ -1,6 +1,6 @@
 /* StarPU --- Runtime system for heterogeneous multicore architectures.
  *
- * Copyright (C) 2009, 2010, 2011  Université de Bordeaux
+ * Copyright (C) 2009, 2010, 2011, 2015  Université de Bordeaux
  * Copyright (C) 2010, 2011  CNRS
  *
  * StarPU is free software; you can redistribute it and/or modify
@@ -162,6 +162,7 @@ static void dump_list(unsigned *x, double *y, struct starpu_perfmodel_history_li
 int _starpu_regression_non_linear_power(struct starpu_perfmodel_history_list *ptr, double *a, double *b, double *c)
 {
 	unsigned n = find_list_size(ptr);
+	STARPU_ASSERT(n);
 
 	unsigned *x = (unsigned *) malloc(n*sizeof(unsigned));
 	STARPU_ASSERT(x);