SCI32: Detect multi-disc audio by RESSCI files instead of RESAUD

If a user fails to rename audio files in the required manner when
copying them, detecting multi-disc audio by looking for a renamed
audio file does not work very well. Looking at RESSCI.00n is a
better choice, though this is not completely valid since e.g.
Rama 1.0 US has only one RESOURCE.SFX volume which its installer
copies to the hard drive, so a little more work will need to be
done in the future to find and fix these kinds of edge cases.

Refs Trac#9976.

engines/sci/resource.cpp

@@ -645,7 +645,7 @@ int ResourceManager::addAppropriateSources() {
 		if (mapFiles.empty() || files.empty())
 			return 0;
 
-		if (Common::File::exists("resaud.001")) {
+		if (Common::File::exists("ressci.001")) {
 			_multiDiscAudio = true;
 		}