SWORD1: Use _missingSubTitleStr when asking for an out of bound textId

It was using textId 0, which is not the subtitle we want anyway. So
instead of using the wrong subtitle, it is probably better to not display
a subtitle at all. A test case for this is with the demo when using
non-english language as several subtitles are missing toward the end.

engines/sword1/objectman.cpp

@@ -105,7 +105,7 @@ char *ObjectMan::lockText(uint32 textId) {
 	addr += sizeof(Header);
 	if ((textId & ITM_ID) >= _resMan->readUint32(addr)) {
 		warning("ObjectMan::lockText(%d): only %d texts in file", textId & ITM_ID, _resMan->readUint32(addr));
-		textId = 0; // get first line instead
+		return _missingSubTitleStr;
 	}
 	uint32 offset = _resMan->readUint32(addr + ((textId & ITM_ID) + 1) * 4);
 	if (offset == 0) {