Resolves https://github.com/zed-industries/zed/issues/55600

This diff fixes `pane::ReopenClosedItem` getting stuck when the
closed-item stack contains entries that cannot be reopened, such as
Project Search, untitled buffers, or Default Settings. Previously,
`Workspace::navigate_history_impl` would pop the newest closed entry and
stop if that item was no longer present in the pane and had no path
recorded for reopening. That made `cmd- shift-t` appear to do nothing
until enough attempts had consumed those unreopenable entries.

With this change, closed-item navigation keeps scanning when it
encounters an entry that cannot be activated or reopened by path. This
preserves the current path-based reopening behavior for normal files,
while avoiding no-op shortcuts caused by non-file items in the closed
stack.

This made me wonder whether or not we'd eventually want full reopen
support for non-traditional items like Project Search or bundled
settings editors. Supporting that properly would require storing
item-specific restoration state, such as search query/options for
Project Search or a bundled-file descriptor for Default Settings, and
teaching closed-item navigation how to recreate those items from that
state. Something definitely out of scope for this PR.

| Before | After |
| --- | --- |
| <video
src="https://github.com/user-attachments/assets/c7044423-4531-4857-84f2-4e9651826c6a"
controls width="500" title="Before"></video> | <video
src="https://github.com/user-attachments/assets/c89dcefb-1796-4cdf-bb21-f165145e678e"
controls width="500" title="After"></video> |

Release Notes:
- Fixed reopening closed tabs getting stuck on closed items that cannot
be reopened.