patch 8.2.0102: messages test fails in small version

Problem:    Messages test fails in small version.
Solution:   Only use test_null_job() when available.

src/testdir/test_messages.vim

@@ -273,8 +273,10 @@ func Test_null()
   echom test_null_list()
   echom test_null_dict()
   echom test_null_blob()
-  echom test_null_job()
   echom test_null_string()
-  echom test_null_channel()
   echom test_null_partial()
+  if has('job')
+    echom test_null_job()
+    echom test_null_channel()
+  endif
 endfunc

src/version.c

@@ -742,6 +742,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    102,
 /**/
     101,
 /**/