Handle empty input in rows_from_file

Closes #808

sqlite_utils/utils.py

@@ -373,6 +373,8 @@ def rows_from_file(
             raise TypeError(
                 "rows_from_file() requires a file-like object that supports peek(), such as io.BytesIO"
             )
+        if not first_bytes:
+            return (), Format.CSV
         if first_bytes.startswith((b"[", b"{")):
             # TODO: Detect newline-JSON
             return rows_from_file(buffered, format=Format.JSON)

tests/test_rows_from_file.py

@@ -20,6 +20,13 @@ def test_rows_from_file_detect_format(input, expected_format):
     assert rows_list == [{"id": "1", "name": "Cleo"}]
 
 
+@pytest.mark.parametrize("input", (b"", b" \n\t"))
+def test_rows_from_file_empty_input(input):
+    rows, format = rows_from_file(BytesIO(input))
+    assert format == Format.CSV
+    assert list(rows) == []
+
+
 @pytest.mark.parametrize(
     "ignore_extras,extras_key,expected",
     (