patch 8.2.3923: Vim9: double free with split argument list in nested function

Problem:    Vim9: double free if a nested function has a line break in the
            argument list.
Solution:   Set cmdlinep when freeing the previous line.

src/testdir/test_vim9_func.vim

@@ -1669,7 +1669,7 @@ def Test_error_in_nested_function()
   assert_fails('FuncWithForwardCall()', 'E1096:', '', 1, 'FuncWithForwardCall')
 enddef
 
-def Test_nested_functin_with_nextcmd()
+def Test_nested_function_with_nextcmd()
   var lines =<< trim END
       vim9script
       # Define an outer function
@@ -1689,6 +1689,24 @@ def Test_nested_functin_with_nextcmd()
   CheckScriptFailure(lines, 'E476: Invalid command: AAAAA')
 enddef
 
+def Test_nested_function_with_args_split()
+  var lines =<< trim END
+      vim9script
+      def FirstFunction()
+        def SecondFunction(
+        )
+        # had a double free if the right parenthesis of the nested function is
+        # on the next line
+         
+        enddef|BBBB
+      enddef
+      # Compile all functions
+      defcompile
+  END
+  # FIXME: this should fail on the BBBB
+  CheckScriptSuccess(lines)
+enddef
+
 def Test_return_type_wrong()
   CheckScriptFailure([
         'def Func(): number',

src/userfunc.c

@@ -219,6 +219,8 @@ get_function_args(
 	    if (theline == NULL)
 		break;
 	    vim_free(*line_to_free);
+	    if (*eap->cmdlinep == *line_to_free)
+		*eap->cmdlinep = theline;
 	    *line_to_free = theline;
 	    whitep = (char_u *)" ";
 	    p = skipwhite(theline);

src/version.c

@@ -749,6 +749,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    3923,
 /**/
     3922,
 /**/