Store: reject path traversal in the store index's "file" field

entry.file comes from the remote store catalog (index.json) and is
joined onto DIRECTORY_GAME verbatim in OnLaunchClick() - Path::operator/
does plain string concatenation with no ".." normalization. On
platforms/builds where the index isn't fetched over HTTPS
(SYSPROP_SUPPORTS_HTTPS false), a network MITM or a compromised store
backend could use a crafted "file" value to make "Launch" boot an
arbitrary host file path instead of the selected store item. Reuse the
existing HasParentDirComponent() helper to reject such entries.

UI/Store.cpp

@@ -34,6 +34,7 @@
 #include "Core/Config.h"
 #include "Core/System.h"
 #include "Core/Util/GameManager.h"
+#include "Core/Util/PathUtil.h"
 #include "UI/EmuScreen.h"
 #include "UI/Store.h"
 
@@ -498,6 +499,12 @@ void StoreScreen::ParseListing(const std::string &json) {
 			const char *file = game.getStringOr("file", nullptr);
 			if (!file)
 				continue;
+			// entry_.file gets joined onto DIRECTORY_GAME verbatim in OnLaunchClick()
+			// (Path::operator/ does no ".." normalization); on platforms/builds where
+			// the store index isn't fetched over HTTPS, a MITM'd or compromised
+			// response could otherwise point "launch" at an arbitrary host path.
+			if (HasParentDirComponent(file))
+				continue;
 			e.file = file;
 			entries_.push_back(e);
 		}