Data Explorer: Relax DuckDB post-query checks to allow queries past t…

…he end of tables (#5644)

Addresses #5552. The frontend in some of its UI calculations requests
the first 10 rows of data, but there may not be 10 rows available. It
might be good to improve the UI logic, but in the meantime there is no
reason to error when a query requests beyond the end of the table.

extensions/positron-duckdb/src/extension.ts

@@ -840,13 +840,9 @@ END`;
 
 		const queryResult = await this.db.runQuery(query);
 
-		// Sanity checks
+		// Sanity check
 		if (queryResult.numCols !== params.columns.length) {
-			return 'Incorrect number of columns in query result';
-		}
-
-		if (queryResult.numRows !== numRows) {
-			return 'Incorrect number of rows in query result';
+			throw new Error('Incorrect number of columns in query result');
 		}
 
 		const result: TableData = {
@@ -881,9 +877,12 @@ END`;
 
 			const fetchValues = (adapter: (field: Vector<any>, i: number) => ColumnValue) => {
 				if ('first_index' in spec) {
+					// There may be fewer rows available than what was requested
+					const lastIndex = Math.min(spec.last_index, queryResult.numRows - 1);
+
 					const columnValues: Array<string | number> = [];
 					// Value range, we need to extract the actual slice requested
-					for (let i = spec.first_index; i <= spec.last_index; ++i) {
+					for (let i = spec.first_index; i <= lastIndex; ++i) {
 						columnValues.push(adapter(field, i));
 					}
 					return columnValues;