workspace: sanitize pinned tab count before usage

Fixes all sorts of panics around usage of incorrect pinned tab count that has been fixed in app itself, yet persists in user db.

Author: osiewicz

crates/workspace/src/pane.rs

@@ -755,7 +755,7 @@ impl Pane {
     }
 
     pub(crate) fn set_pinned_count(&mut self, count: usize) {
-        self.pinned_tab_count = count;
+        self.pinned_tab_count = count.min(self.items.len());
     }
 
     pub(crate) fn pinned_count(&self) -> usize {
@@ -1890,7 +1890,7 @@ impl Pane {
     fn unpin_tab_at(&mut self, ix: usize, cx: &mut ViewContext<'_, Self>) {
         maybe!({
             let pane = cx.view().clone();
-            self.pinned_tab_count = self.pinned_tab_count.checked_sub(1).unwrap();
+            self.pinned_tab_count = self.pinned_tab_count.checked_sub(1)?;
             let destination_index = self.pinned_tab_count;
 
             let id = self.item_for_index(ix)?.item_id();