Sas: Correct calculation of VAG end.

Not sure why everything is negative one indexed, but this prevents reading
beyond the size of the buffer.

This shouldn't change sound output, but it may fix a crash if VAG is at
the edge of memory (unlikely, though.)

Core/HW/SasAudio.cpp

@@ -65,6 +65,11 @@ void VagDecoder::Start(u32 data, u32 vagSize, bool loopEnabled) {
 }
 
 void VagDecoder::DecodeBlock(u8 *&read_pointer) {
+	if (curBlock_ == numBlocks_ - 1) {
+		end_ = true;
+		return;
+	}
+
 	u8 *readp = read_pointer;
 	int predict_nr = *readp++;
 	int shift_factor = predict_nr & 0xf;
@@ -106,9 +111,6 @@ void VagDecoder::DecodeBlock(u8 *&read_pointer) {
 	s_2 = s2;
 	curSample = 0;
 	curBlock_++;
-	if (curBlock_ == numBlocks_) {
-		end_ = true;
-	}
 
 	read_pointer = readp;
 }