SCUMM: Do not pass non-string literal but "%s" + string to displayMes…

…sage.

Since displayMessages usualy vsnprintf internally it is not quite safe to pass
any string to it, since it might include a format argument like %n, which is
unsafe.

engines/scumm/scumm.cpp

@@ -2494,7 +2494,7 @@ void ScummEngine_v90he::runBootscript() {
 
 void ScummEngine::startManiac() {
 	debug(0, "stub startManiac()");
-	displayMessage(0, _("Usually, Maniac Mansion would start now. But ScummVM doesn't do that yet. To play it, go to 'Add Game' in the ScummVM start menu and select the 'Maniac' directory inside the Tentacle game directory."));
+	displayMessage(0, "%s", _("Usually, Maniac Mansion would start now. But ScummVM doesn't do that yet. To play it, go to 'Add Game' in the ScummVM start menu and select the 'Maniac' directory inside the Tentacle game directory."));
 }
 
 #pragma mark -