[console] Unhook hooked functions on shutdown

Forgetting to unhook the functions (Sys_Printf and the client console's
input event handler) was not a problem for static builds because the
functions were always present, but in builds with dynamic plugins, the
client console's code got ripped away and thus Sys_Printf and the event
hander were being sent into invalid memory. Too much work, not enough
play (with a fully installed client).

libs/console/client.c

@@ -952,6 +952,7 @@ C_Init (void)
 static void
 C_shutdown (void)
 {
+	IE_Remove_Handler (con_event_id);
 }
 
 static general_funcs_t plugin_info_general_funcs = {

libs/console/console.c

@@ -57,6 +57,7 @@ static U void (*const display)(const char **, int) = Con_DisplayList;
 #undef U
 
 static cvar_t *con_interpreter;
+static sys_printf_t saved_sys_printf;
 
 static void
 Con_Interp_f (cvar_t *var)
@@ -89,6 +90,9 @@ Con_Interp_f (cvar_t *var)
 static void
 Con_shutdown (void *data)
 {
+	if (saved_sys_printf) {
+		Sys_SetStdPrintf (saved_sys_printf);
+	}
 	if (con_module) {
 		con_module->functions->general->shutdown ();
 		PI_UnloadPlugin (con_module);
@@ -102,7 +106,8 @@ Con_Init (const char *plugin_name)
 
 	con_module = PI_LoadPlugin ("console", plugin_name);
 	if (con_module) {
-		Sys_SetStdPrintf (con_module->functions->console->print);
+		__auto_type funcs = con_module->functions->console;
+		saved_sys_printf = Sys_SetStdPrintf (funcs->print);
 	} else {
 		setvbuf (stdout, 0, _IOLBF, BUFSIZ);
 	}

libs/util/sys.c

@@ -247,6 +247,9 @@ VISIBLE sys_printf_t
 Sys_SetStdPrintf (sys_printf_t func)
 {
 	sys_printf_t prev = sys_std_printf_function;
+	if (!func) {
+		func = Sys_StdPrintf;
+	}
 	sys_std_printf_function = func;
 	return prev;
 }
@@ -255,6 +258,9 @@ VISIBLE sys_printf_t
 Sys_SetErrPrintf (sys_printf_t func)
 {
 	sys_printf_t prev = sys_err_printf_function;
+	if (!func) {
+		func = Sys_ErrPrintf;
+	}
 	sys_err_printf_function = func;
 	return prev;
 }