fix non existant paths not being sanitized properly on Linux

Author: NotHyper-474

source/funkin/util/FileUtil.hx

@@ -58,7 +58,7 @@ class FileUtil
    */
   public static var PROTECTED_PATHS(get, never):Array<String>;
 
-  public static function get_PROTECTED_PATHS():Array<String>
+  static function get_PROTECTED_PATHS():Array<String>
   {
     final protected:Array<String> = [
       '',
@@ -83,7 +83,8 @@ class FileUtil
     #if sys
     for (i in 0...protected.length)
     {
-      protected[i] = sys.FileSystem.fullPath(Path.join([gameDirectory, protected[i]]));
+      // On Linux 'fullPath' just makes most of these null which actually just makes the paths unprotected
+      protected[i] = #if !linux sys.FileSystem.fullPath #end (Path.join([gameDirectory, protected[i]]));
     }
     #end
 
@@ -1306,8 +1307,26 @@ class FileUtilSandboxed
 
     #if sys
     // TODO: figure out how to get "real" path of symlinked paths
-    final realPath:String = sys.FileSystem.fullPath(Path.join([FileUtil.gameDirectory, sanitized.join('/')]));
-    if (!realPath.startsWith(FileUtil.gameDirectory))
+    #if linux
+    // The implementation on Linux fails if the path doesn't exist
+    var realPath:Null<String> = null;
+    var unresolvedSegments:Array<String> = [];
+    while (realPath == null && sanitized.length > 0)
+    {
+      realPath = sys.FileSystem.fullPath(Path.join([FileUtil.gameDirectory].concat(sanitized)));
+      if (realPath == null) unresolvedSegments.unshift(sanitized.pop() ?? continue);
+    }
+
+    if (unresolvedSegments.length > 0)
+    {
+      if (realPath != null) unresolvedSegments.unshift(realPath);
+      realPath = Path.join(unresolvedSegments);
+    }
+    #else
+    final realPath:Null<String> = sys.FileSystem.fullPath(Path.join([FileUtil.gameDirectory].concat(sanitized)));
+    #end
+
+    if (realPath == null || !realPath.startsWith(FileUtil.gameDirectory))
     {
       return FileUtil.gameDirectory;
     }