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)

src/version.c

@@ -792,6 +792,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    502,
 /**/
     501,
 /**/