cmdutils: add a macro to simplify grow_array() calls.

cmdutils.h

@@ -418,6 +418,9 @@ FILE *get_preset_file(char *filename, size_t filename_size,
  */
 void *grow_array(void *array, int elem_size, int *size, int new_size);
 
+#define GROW_ARRAY(array, nb_elems)\
+    array = grow_array(array, sizeof(*array), &nb_elems, nb_elems + 1)
+
 typedef struct FrameBuffer {
     uint8_t *base[4];
     uint8_t *data[4];