patch 8.2.3951: Vim9: memory leak when text after a nested function

Problem:    Vim9: memory leak when text after a nested function.
Solution:   Free the function if text is found after "enddef".

src/testdir/test_vim9_func.vim

@@ -1493,9 +1493,20 @@ def Test_call_varargs_only()
 enddef
 
 def Test_using_var_as_arg()
-  writefile(['def Func(x: number)',  'var x = 234', 'enddef', 'defcompile'], 'Xdef')
-  assert_fails('so Xdef', 'E1006:', '', 1, 'Func')
-  delete('Xdef')
+  var lines =<< trim END
+      def Func(x: number)
+        var x = 234
+      enddef
+  END
+  CheckDefFailure(lines, 'E1006:')
+
+  lines =<< trim END
+      def Func(Ref: number)
+        def Ref()
+        enddef
+      enddef
+  END
+  CheckDefFailure(lines, 'E1073:')
 enddef
 
 def DictArg(arg: dict<string>)

src/version.c

@@ -749,6 +749,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    3951,
 /**/
     3950,
 /**/

src/vim9compile.c

@@ -889,6 +889,7 @@ compile_nested_function(exarg_T *eap, cctx_T *cctx, char_u **line_to_free)
 	semsg(_(e_text_found_after_str_str),
 	      eap->cmdidx == CMD_def ? "enddef" : "endfunction", eap->nextcmd);
 	r = FAIL;
+	func_ptr_unref(ufunc);
 	goto theend;
     }