Be friendlier when trying to but from empty DVD drives.

git-svn-id: https://dolphin-emu.googlecode.com/svn/trunk@2422 8ced0084-cf51-0410-be5f-012b33b47a6e

Source/Core/DiscIO/Src/DriveBlob.h

@@ -36,9 +36,11 @@ private:
 
 #ifdef _WIN32
 	HANDLE hDisc;
-	PREVENT_MEDIA_REMOVAL	pmrLockCDROM;
+	PREVENT_MEDIA_REMOVAL pmrLockCDROM;
+	bool IsOK() {return hDisc != INVALID_HANDLE_VALUE;}
 #else
 	FILE* file_;
+	bool IsOK() {return file_ != 0;}
 #endif
 	s64 size;
 	u64 *block_pointers;