Revert "GRAPHICS: do not clear the internal state of IFFDecoder on loadStream()."

This reverts commit 92c1ff31d6.

graphics/decoders/iff.cpp

@@ -59,8 +59,7 @@ void IFFDecoder::destroy() {
 }
 
 bool IFFDecoder::loadStream(Common::SeekableReadStream &stream) {
-	// NOTE: we cannot call destroy() here, like most other decoders do, otherwise the 
-	// settings (stored in _numRelevantPlanes and _pixelPacking) will be cleared.
+	destroy();
 
 	const uint32 form = stream.readUint32BE();