patch 8.2.0104: using channel or job with ":execute" has strange effects

Problem:    Using channel or job with ":execute" has strange effects.
Solution:   Give an error message for Job and Channel.

Author: brammool

src/eval.c

@@ -6055,7 +6055,15 @@ ex_execute(exarg_T *eap)
 	    char_u   buf[NUMBUFLEN];
 
 	    if (eap->cmdidx == CMD_execute)
-		p = tv_get_string_buf(&rettv, buf);
+	    {
+		if (rettv.v_type == VAR_CHANNEL || rettv.v_type == VAR_JOB)
+		{
+		    emsg(_(e_inval_string));
+		    p = NULL;
+		}
+		else
+		    p = tv_get_string_buf(&rettv, buf);
+	    }
 	    else
 		p = tv_stringify(&rettv, buf);
 	    if (p == NULL)

src/testdir/test_eval_stuff.vim

@@ -216,3 +216,15 @@ func Test_scriptversion_fail()
   call assert_fails('source Xversionscript', 'E999:')
   call delete('Xversionscript')
 endfunc
+
+func Test_excute_null()
+  call assert_fails('execute test_null_list()', 'E730:')
+  call assert_fails('execute test_null_dict()', 'E731:')
+  call assert_fails('execute test_null_blob()', 'E976:')
+  execute test_null_string()
+  call assert_fails('execute test_null_partial()', 'E729:')
+  if has('job')
+    call assert_fails('execute test_null_job()', 'E908:')
+    call assert_fails('execute test_null_channel()', 'E908:')
+  endif
+endfunc

src/version.c

@@ -742,6 +742,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    104,
 /**/
     103,
 /**/