patch 8.0.0561: undefined behavior when using backslash after empty line

Problem:    Undefined behavior when using backslash after empty line.
Solution:   Check for an empty line. (Dominique Pelle, closes #1631)
diff --git a/src/version.c b/src/version.c
index 325be55..91ef1f3 100644
--- a/src/version.c
+++ b/src/version.c
@@ -765,6 +765,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    561,
+/**/
     560,
 /**/
     559,