patch 9.0.0558: Coverity warns for possibly using NULL pointer

Problem:    Coverity warns for possibly using NULL pointer.
Solution:   Only use "evalarg" when not NULL.
diff --git a/src/version.c b/src/version.c
index f01afe3..48f2ca5 100644
--- a/src/version.c
+++ b/src/version.c
@@ -700,6 +700,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    558,
+/**/
     557,
 /**/
     556,