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)

src/ex_getln.c

@@ -682,7 +682,8 @@ may_add_char_to_search(int firstc, int *c, incsearch_state_T *is_state)
     // 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 @@ open_cmdwin(void)
 	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);

src/testdir/dumps/Test_cmdwin_interrupted.dump

@@ -0,0 +1,18 @@
+> +0&#ffffff0@74
+|~+0#4040ff13&| @73
+|~| @73
+|~| @73
+|~| @73
+|~| @73
+|~| @73
+|~| @73
+|~| @73
+|~| @73
+|~| @73
+|~| @73
+|~| @73
+|~| @73
+|~| @73
+|~| @73
+|~| @73
+|d+0#0000000&|o|n|e| @52|0|,|0|-|1| @8|A|l@1| 

src/testdir/test_cmdline.vim

@@ -1183,6 +1183,33 @@ func Test_cmdwin_jump_to_win()
   call assert_equal(1, winnr('$'))
 endfunc
 
+func Test_cmdwin_interrupted()
+  CheckScreendump
+
+  " aborting the :smile output caused the cmdline window to use the current
+  " buffer.
+  let lines =<< trim [SCRIPT]
+    au WinNew * smile
+  [SCRIPT]
+  call writefile(lines, 'XTest_cmdwin')
+
+  let buf = RunVimInTerminal('-S XTest_cmdwin', {'rows': 18})
+  call TermWait(buf, 1000)
+  " open cmdwin
+  call term_sendkeys(buf, "q:")
+  call TermWait(buf, 500)
+  " quit more prompt for :smile command
+  call term_sendkeys(buf, "q")
+  call TermWait(buf, 500)
+  " execute a simple command
+  call term_sendkeys(buf, "aecho 'done'\<CR>")
+  call VerifyScreenDump(buf, 'Test_cmdwin_interrupted', {})
+
+  " clean up
+  call StopVimInTerminal(buf)
+  call delete('XTest_cmdwin')
+endfunc
+
 " Test for backtick expression in the command line
 func Test_cmd_backtick()
   %argd

src/version.c

@@ -754,6 +754,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    911,
 /**/
     910,
 /**/