fix: Copy symlink as symlink in snapshot compare

When comparing snapshots, copy symlinks in the snapshots as symlinks, not as
their target.  The old behavior made the comparison not fully compare the actual
snapshot data and, even worse, could fill up your entire disk (when having
circular symlinks, e.g. a symlink to `/`, which copies `/` and eventually
copies the original symlink which points to `/` which ...).

Additionally fixes a crash when the compared snapshot(s) contain a symlink
pointing to a nonexistent target.

Fixes bit-team#1902.

CHANGES

@@ -1,6 +1,8 @@
 Back In Time
 
 Version 1.6.0-dev (development of upcoming release)
+* Fix: Copy symlink as symlink in snapshot compare (#1902) (Peter Sevens @sevens)
+       Additionally fixes a crash when comparing a snapshot with a symlink pointing to a nonexistent target.
 * ...
 
 Version 1.5.3 (2024-11-13)

qt/app.py

@@ -1722,7 +1722,7 @@ def tmpCopy(self, full_path, sid = None):
         tmp_file = os.path.join(d.name, os.path.basename(full_path))
 
         if os.path.isdir(full_path):
-            shutil.copytree(full_path, tmp_file)
+            shutil.copytree(full_path, tmp_file, symlinks=True)
         else:
             shutil.copy(full_path, d.name)