patch 8.1.0502: internal diff fails when diffing a context diff

Problem:    Internal diff fails when diffing a context diff. (Hirohito Higashi)
Solution:   Only use callback calls with one line. (closes #3581)
diff --git a/src/version.c b/src/version.c
index 73d0621..d2bed0e 100644
--- a/src/version.c
+++ b/src/version.c
@@ -793,6 +793,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    502,
+/**/
     501,
 /**/
     500,