patch 8.2.0911: crash when opening a buffer for the cmdline window fails

Problem:    Crash when opening a buffer for the cmdline window fails. (Chris
            Barber)
Solution:   Check do_ecmd() succeeds.  Reset got_int if "q" was used at the
            more prompt. (closes #6211)
diff --git a/src/ex_getln.c b/src/ex_getln.c
index 48d40cf..c003748 100644
--- a/src/ex_getln.c
+++ b/src/ex_getln.c
@@ -682,7 +682,8 @@
     // NOTE: must call restore_last_search_pattern() before returning!
     save_last_search_pattern();
 
-    if (!do_incsearch_highlighting(firstc, &search_delim, is_state, &skiplen, &patlen))
+    if (!do_incsearch_highlighting(firstc, &search_delim, is_state,
+							    &skiplen, &patlen))
     {
 	restore_last_search_pattern();
 	return FAIL;
@@ -4205,10 +4206,19 @@
 	ga_clear(&winsizes);
 	return K_IGNORE;
     }
-    cmdwin_type = get_cmdline_type();
+    // Don't let quitting the More prompt make this fail.
+    got_int = FALSE;
 
     // Create the command-line buffer empty.
-    (void)do_ecmd(0, NULL, NULL, NULL, ECMD_ONE, ECMD_HIDE, NULL);
+    if (do_ecmd(0, NULL, NULL, NULL, ECMD_ONE, ECMD_HIDE, NULL) == FAIL)
+    {
+	// Some autocommand messed it up?
+	win_close(curwin, TRUE);
+	ga_clear(&winsizes);
+	return Ctrl_C;
+    }
+    cmdwin_type = get_cmdline_type();
+
     apply_autocmds(EVENT_BUFFILEPRE, NULL, NULL, FALSE, curbuf);
     (void)setfname(curbuf, (char_u *)"[Command Line]", NULL, TRUE);
     apply_autocmds(EVENT_BUFFILEPOST, NULL, NULL, FALSE, curbuf);