fix: raise NoTable from rows_where() and delete_where() for non-existent tables

rows_where() silently returned an empty iterator and delete_where()
silently returned self when called on a table that does not exist.
This masked bugs in callers that passed a wrong table name.  Both
methods now raise NoTable (matching the behaviour of count_where()
and duplicate()), as planned for the v5 release.

tests/test_delete.py

@@ -1,4 +1,6 @@
+import pytest
 import sqlite_utils
+from sqlite_utils.db import NoTable
 
 
 def test_delete_rowid_table(fresh_db):
@@ -62,3 +64,8 @@ def test_delete_where_analyze(fresh_db):
     assert list(fresh_db.table("sqlite_stat1").rows) == [
         {"tbl": "table", "idx": "idx_table_i", "stat": "6 1"}
     ]
+
+
+def test_delete_where_nonexistent_table(fresh_db):
+    with pytest.raises(NoTable):
+        fresh_db.table("does_not_exist").delete_where()

tests/test_rows.py

@@ -147,3 +147,9 @@ def test_pks_and_rows_where_compound_pk_declaration_order(fresh_db):
     fresh_db.table("t").insert({"a": "A", "b": "B"})
     pks_and_rows = list(fresh_db.table("t").pks_and_rows_where())
     assert pks_and_rows == [(("A", "B"), {"b": "B", "a": "A"})]
+
+
+def test_rows_where_nonexistent_table_raises(fresh_db):
+    from sqlite_utils.db import NoTable
+    with pytest.raises(NoTable):
+        list(fresh_db.table("does_not_exist").rows_where())