Fix RewindAwait branching when cursor is empty

Even if we have a page, the cursor can still be empty if there are no
records.

core/btree.rs

@@ -108,7 +108,7 @@ impl BTreeCursor {
 
 impl Cursor for BTreeCursor {
     fn is_empty(&self) -> bool {
-        self.page.borrow().is_none()
+        self.record.borrow().is_none()
     }
 
     fn rewind(&mut self) -> Result<CursorResult<()>> {
@@ -147,8 +147,4 @@ impl Cursor for BTreeCursor {
     fn record(&self) -> Result<Ref<Option<OwnedRecord>>> {
         Ok(self.record.borrow())
     }
-
-    fn has_record(&self) -> bool {
-        self.record.borrow().is_some()
-    }
 }

core/types.rs

@@ -87,5 +87,4 @@ pub trait Cursor {
     fn wait_for_completion(&mut self) -> Result<()>;
     fn rowid(&self) -> Result<Ref<Option<u64>>>;
     fn record(&self) -> Result<Ref<Option<OwnedRecord>>>;
-    fn has_record(&self) -> bool;
 }

core/vdbe.rs

@@ -288,7 +288,7 @@ impl Program {
                 } => {
                     let cursor = cursors.get_mut(cursor_id).unwrap();
                     cursor.wait_for_completion()?;
-                    if cursor.has_record() {
+                    if !cursor.is_empty() {
                         state.pc = *pc_if_next;
                     } else {
                         state.pc += 1;