patch 8.2.0836: not all :cdo output is visible

Problem:    Not all :cdo output is visible.
Solution:   Reset 'shortmess' temporarily. (Yegappan Lakshmanan, closes #6155)
diff --git a/src/ex_cmds2.c b/src/ex_cmds2.c
index a0f3839..cd066f5 100644
--- a/src/ex_cmds2.c
+++ b/src/ex_cmds2.c
@@ -643,7 +643,13 @@
 
 		qf_idx = qf_get_cur_idx(eap);
 
+		// Clear 'shm' to avoid that the file message overwrites
+		// any output from the command.
+		p_shm_save = vim_strsave(p_shm);
+		set_option_value((char_u *)"shm", 0L, (char_u *)"", 0);
 		ex_cnext(eap);
+		set_option_value((char_u *)"shm", 0L, p_shm_save, 0);
+		vim_free(p_shm_save);
 
 		// If jumping to the next quickfix entry fails, quit here
 		if (qf_get_cur_idx(eap) == qf_idx)