Get rid of warnings creating MemStick, etc.

Common/FileUtil.cpp

@@ -202,12 +202,12 @@ bool CreateFullPath(const std::string &fullPath)
 		// we're done, yay!
 		if (position == fullPath.npos)
 		{
-			if (!File::IsDirectory(fullPath))
+			if (!File::Exists(fullPath))
 				File::CreateDir(fullPath);
 			return true;
 		}
 		std::string subPath = fullPath.substr(0, position);
-		if (!File::IsDirectory(subPath))
+		if (!File::Exists(subPath))
 			File::CreateDir(subPath);
 
 		// A safety check