Disable diff hunks for untracked files, even w/ no newline at eof (#25980)

This fixes an issue where diff hunks were shown for untracked files, but
only if the files did not end with a newline.

Release Notes:

- N/A

crates/multi_buffer/src/multi_buffer_tests.rs

@@ -2274,7 +2274,7 @@ impl ReferenceMultibuffer {
                 }
 
                 if !hunk.buffer_range.start.is_valid(&buffer) {
-                    log::trace!("skipping hunk with deleted start: {:?}", hunk.row_range);
+                    log::trace!("skipping hunk with deleted start: {:?}", hunk.range);
                     continue;
                 }