patch 8.2.1706: Vim9: crash after running into the "Multiple closures" error

Problem:    Vim9: crash after running into the "Multiple closures" error.
Solution:   When a function fails still update any closures. (closes #6973)

src/testdir/test_vim9_func.vim

@@ -1294,6 +1294,20 @@ def Test_call_closure_not_compiled()
   GetResult(g:Ref)->assert_equal('sometext')
 enddef
 
+def Test_double_closure_fails()
+  let lines =<< trim END
+    vim9script
+    def Func()
+    let var = 0
+    for i in range(2)
+	timer_start(0, {-> var})
+    endfor
+    enddef
+    Func()
+  END
+  CheckScriptFailure(lines, 'Multiple closures not supported yet')
+enddef
+
 def Test_sort_return_type()
   let res: list<number>
   res = [1, 2, 3]->sort()

src/version.c

@@ -750,6 +750,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1706,
 /**/
     1705,
 /**/

src/vim9execute.c

@@ -2676,15 +2676,11 @@ call_def_function(
 	continue;
 
 func_return:
-	// Restore previous function. If the frame pointer is zero then there
-	// is none and we are done.
+	// Restore previous function. If the frame pointer is where we started
+	// then there is none and we are done.
 	if (ectx.ec_frame_idx == initial_frame_idx)
-	{
-	    if (handle_closure_in_use(&ectx, FALSE) == FAIL)
-		// only fails when out of memory
-		goto failed;
 	    goto done;
-	}
+
 	if (func_return(&ectx) == FAIL)
 	    // only fails when out of memory
 	    goto failed;
@@ -2703,6 +2699,10 @@ done:
     ret = OK;
 
 failed:
+    // Also deal with closures when failed, they may already be in use
+    // somewhere.
+    handle_closure_in_use(&ectx, FALSE);
+
     // When failed need to unwind the call stack.
     while (ectx.ec_frame_idx != initial_frame_idx)
 	func_return(&ectx);