Fix panic when starting helix tutor (#11352)

Closes #11351

Also fixed some minor issues related to log
message contents, and removed unnecessary use
of `.as_mut()` as per code review comments on
the PR.

helix-view/src/document.rs

@@ -1080,7 +1080,8 @@ impl Document {
     }
 
     pub fn pickup_last_saved_time(&mut self) {
-        self.last_saved_time = match self.path.as_mut().unwrap().metadata() {
+        self.last_saved_time = match self.path().as_mut() {
+            Some(path) => match path.metadata() {
                 Ok(metadata) => match metadata.modified() {
                     Ok(mtime) => mtime,
                     Err(_) => {
@@ -1096,6 +1097,8 @@ impl Document {
                     );
                     SystemTime::now()
                 }
+            },
+            None => SystemTime::now(),
         };
     }