patch 8.2.0018: :join does not add white space where it should

Problem:    :join does not add white space where it should. (Zdenek Dohnal)
Solution:   Handle joining multiple lines propely.

src/version.c

@@ -742,6 +742,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    18,
 /**/
     17,
 /**/