patch 9.1.1884: :defer an empty lambda causes a crash

Problem:  :defer an empty lambda causes a crash
          (Maxim Kim, after v9.1.1882)
Solution: Check for missing arguments (Yegappan Lakshmanan)

related: #18641
closes: #18653

Signed-off-by: Yegappan Lakshmanan <[email protected]>
Signed-off-by: Christian Brabandt <[email protected]>

Author: yegappan

src/testdir/test_vim9_script.vim

@@ -5343,6 +5343,18 @@ def Test_defer_lambda_func()
     defcompile
   END
   v9.CheckScriptFailure(lines, 'E1028: Compiling :def function failed', 1)
+
+  # Error: lambda without arguments
+  lines =<< trim END
+    vim9script
+    def Foo()
+      defer () => {
+      }
+      assert_report("shouldn't reach here")
+    enddef
+    defcompile
+  END
+  v9.CheckScriptFailure(lines, 'E107: Missing parentheses: ', 1)
 enddef
 
 " Test for using an non-existing type in a "for" statement.

src/version.c

@@ -729,6 +729,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1884,
 /**/
     1883,
 /**/

src/vim9cmds.c

@@ -2047,7 +2047,12 @@ compile_defer(char_u *arg_start, cctx_T *cctx)
 	// a lambda function
 	if (compile_lambda(&arg, cctx) != OK)
 	    return NULL;
-	paren = arg;
+	paren = vim_strchr(arg, '(');
+	if (paren == NULL)
+	{
+	    semsg(_(e_missing_parenthesis_str), arg);
+	    return NULL;
+	}
     }
     else
     {