I believe this is a security feature i.e. one should not be able to read the original file path of a file input into a browser form. File input is for reading file contents only.
Now coming to how can we solve this answer is use FileReader's readAsDataURL something like following in JavaScript
document.getElementById("myUploadInput").addEventListener("change", function() {
var reader = new FileReader();
reader.readAsDataURL(document.getElementById("myUploadInput").files[0]);
});
Or something very similar, I dont have the access to the code so only can make a guess...