patch 9.1.0471: Crash when using autocmd_get() after removing event inside autocmd

Problem:  Crash when using autocmd_get() after removing event inside
          autocmd (Sergey Vlasov)
Solution: Check that the pattern is NULL (zeertzjq).

fixes: #14937
closes: #14939

Signed-off-by: zeertzjq <zeertzjq@outlook.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

src/autocmd.c

@@ -3391,6 +3391,9 @@ f_autocmd_get(typval_T *argvars, typval_T *rettv)
 	{
 	    char_u	*group_name;
 
+	    if (ap->pat == NULL)		// pattern has been removed
+		continue;
+
 	    if (group != AUGROUP_ALL && group != ap->group)
 		continue;
 

src/testdir/test_autocmd.vim

@@ -4024,6 +4024,32 @@ func Test_autocmd_get()
         \ event: 'BufAdd', pattern: '*.abc'}))
   call assert_equal([], autocmd_get(#{group: 'TestAutoCmdFns',
         \ event: 'BufWipeout'}))
+
+  " Test for getting autocmds after removing one inside an autocmd
+  func CheckAutocmdGet()
+    augroup TestAutoCmdFns
+      autocmd! BufAdd *.vim
+    augroup END
+
+    let expected = [
+          \ #{cmd: 'echo "bufadd-py"', group: 'TestAutoCmdFns',
+          \  pattern: '*.py', nested: v:false, once: v:false,
+          \  event: 'BufAdd'},
+          \ #{cmd: 'echo "bufhidden"', group: 'TestAutoCmdFns',
+          \  pattern: '*.vim', nested: v:false,
+          \  once: v:false, event: 'BufHidden'}]
+
+    call assert_equal(expected, autocmd_get(#{group: 'TestAutoCmdFns'}))
+    call assert_equal([expected[0]],
+          \ autocmd_get(#{group: 'TestAutoCmdFns', pattern: '*.py'}))
+    call assert_equal([expected[1]],
+          \ autocmd_get(#{group: 'TestAutoCmdFns', pattern: '*.vim'}))
+  endfunc
+
+  autocmd User Xauget call CheckAutocmdGet()
+  doautocmd User Xauget
+  autocmd! User Xauget
+
   call assert_fails("call autocmd_get(#{group: 'abc', event: 'BufAdd'})",
         \ 'E367:')
   let cmd = "echo autocmd_get(#{group: 'TestAutoCmdFns', event: 'abc'})"

src/version.c

@@ -704,6 +704,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    471,
 /**/
     470,
 /**/