Make command-repeat work after gdb.execute

Since commit

  56bcdbea2b ("Let gdb.execute handle multi-line commands")

command repetition after using the `gdb.execute` Python function
fails (the previous command is not repeated anymore). This happens
because read_command_lines_1 sets dont_repeat, but the call to
prevent_dont_repeat in execute_gdb_command is later.

The fix is to move the call to prevent_dont_repeat to the beginning of
the function.

Tested on my laptop (ArchLinux-x86_64).

gdb/ChangeLog:

	PR python/23714
	* gdb/python/python.c (execute_gdb_command): Call
	prevent_dont_repeat earlier to avoid affecting dont_repeat.

gdb/testuite/ChangeLog:

	PR python/23714
	* gdb.python/python.exp: Test command repetition after
	gdb.execute.

gdb/python/python.c

@@ -583,6 +583,8 @@ execute_gdb_command (PyObject *self, PyObject *args, PyObject *kw)
 
   std::string to_string_res;
 
+  scoped_restore preventer = prevent_dont_repeat ();
+
   TRY
     {
       struct interp *interp;
@@ -612,7 +614,6 @@ execute_gdb_command (PyObject *self, PyObject *args, PyObject *kw)
 	interp = interp_lookup (current_ui, "console");
 	current_uiout = interp->interp_ui_out ();
 
-	scoped_restore preventer = prevent_dont_repeat ();
 	if (to_string)
 	  to_string_res = execute_control_commands_to_string (lines.get (),
 							      from_tty);