File Open dlg: "Open" button is grayed out for existed file

Suppose the "test.diffExtension" is entered in the "File name :" column and  "All Files *" is selected in file type , the "Open" button is grayed out.

To arrive at this scenario , copy the file name and paste it to the File name field in the "Open File" window , and then change file type to All Files, the Open button will remain grayed out.
When there are about 1000 files with similar looking file names in the working directory , and one cannot search for it visually and click on the file name , to activate the "Open" button.
So first reaction that the file does not exist in the directory since the "Open" button is grayed out.

Can this be enhanced so that the "Open" button becomes active.