Mutex around PBP file access.

There's some thread safety issue in there, this makes it so we can read
thumbnails without crashing sometimes - fixes #7330.

Core/FileSystems/BlockDevices.cpp

@@ -344,9 +344,12 @@ bool CISOFileBlockDevice::ReadBlocks(u32 minBlock, int count, u8 *outPtr) {
 }
 
 
+recursive_mutex NPDRMDemoBlockDevice::mutex_;
+
 NPDRMDemoBlockDevice::NPDRMDemoBlockDevice(FileLoader *fileLoader)
 	: fileLoader_(fileLoader)
 {
+	lock_guard guard(mutex_);
 	MAC_KEY mkey;
 	CIPHER_KEY ckey;
 	u8 np_header[256];
@@ -412,6 +415,7 @@ NPDRMDemoBlockDevice::NPDRMDemoBlockDevice(FileLoader *fileLoader)
 
 NPDRMDemoBlockDevice::~NPDRMDemoBlockDevice()
 {
+	lock_guard guard(mutex_);
 	delete [] table;
 	delete [] tempBuf;
 	delete [] blockBuf;
@@ -421,6 +425,7 @@ int lzrc_decompress(void *out, int out_len, void *in, int in_len);
 
 bool NPDRMDemoBlockDevice::ReadBlock(int blockNumber, u8 *outPtr)
 {
+	lock_guard guard(mutex_);
 	CIPHER_KEY ckey;
 	int block, lba, lzsize;
 	size_t readSize;