Fixed the NVR close mess - all machines now work again.

src/machine/machine_table.c

@@ -220,5 +220,6 @@ machine_get_machine_from_internal_name(char *s)
 void
 machine_close(void)
 {
-    machines[machine].nvr_close();
+    if (machines[machine].nvr_close)
+    	machines[machine].nvr_close();
 }

src/nvr_at.c

@@ -76,6 +76,9 @@ nvr_read(uint16_t addr, void *priv)
 void
 nvr_at_close(void)
 {
+    if (nvrp == NULL)
+	return;
+
     if (nvrp->fname != NULL)
 	free(nvrp->fname);