Fix shared lock rejection bug in do_LOCK

Removed blanket rejection of lock requests on already-locked resources.
The do_LOCK method was returning 423 for all new lock requests on
locked resources without checking lock compatibility. This prevented
multiple shared locks from being acquired.

The fix delegates compatibility checking to _lock_unlock_create(),
which already has logic to validate exclusive vs shared lock conflicts.

Changes:
- locks.py: Removed lines 157-160 that returned 423 for all lock
  requests on locked resources
- locks.py: Added try/catch around _lock_unlock_create() to handle
  incompatible lock exceptions

Test results:
- double_sharedlock (test 27): now passing
- Locks test suite: improved from 32/37 to 33/37 (89.2%)

Remaining failures (tests 32-34) are related to collection locking,
which the code explicitly notes is not yet supported (locks.py:85-87).

Author: pi-anl

pywebdav/lib/locks.py

@@ -154,25 +154,25 @@ def do_LOCK(self):
         alreadylocked = self._l_isLocked(uri)
         log.info('do_LOCK: alreadylocked = %s' % alreadylocked)
 
-        if body and alreadylocked:
-            # Full LOCK request but resource already locked
-            self.responses[423] = ('Locked', 'Already locked')
-            return self.send_status(423)
-
-        elif body and not ifheader:
+        if body and not ifheader:
             # LOCK with XML information
             data = self._lock_unlock_parse(body)
-            token, result = self._lock_unlock_create(uri, 'unknown', depth, data)
-
-            if result:
-                self.send_body(bytes(result, 'utf-8'), 207, 'Error', 'Error',
-                                'text/xml; charset="utf-8"')
-
-            else:
-                lock = self._l_getLock(token)
-                self.send_body(bytes(lock.asXML(), 'utf-8'), 200, 'OK', 'OK',
-                                'text/xml; charset="utf-8"',
-                                {'Lock-Token' : '<opaquelocktoken:%s>' % token})
+            try:
+                token, result = self._lock_unlock_create(uri, 'unknown', depth, data)
+
+                if result:
+                    self.send_body(bytes(result, 'utf-8'), 207, 'Error', 'Error',
+                                    'text/xml; charset="utf-8"')
+                else:
+                    lock = self._l_getLock(token)
+                    self.send_body(bytes(lock.asXML(), 'utf-8'), 200, 'OK', 'OK',
+                                    'text/xml; charset="utf-8"',
+                                    {'Lock-Token' : '<opaquelocktoken:%s>' % token})
+            except Exception as e:
+                # Lock creation failed (e.g., incompatible lock exists)
+                log.info(f'Lock creation failed: {e}')
+                self.responses[423] = ('Locked', str(e))
+                return self.send_status(423)
 
 
         else: