Fix enum zero strict mode validation to match MySQL exactly

After MySQL comparison server testing, corrected logic to reject 0 values
in strict mode regardless of enum definition, matching MySQL behavior exactly.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

Author: elianddb

enginetest/queries/script_queries.go

@@ -8715,10 +8715,8 @@ where
 				},
 			},
 			{
-				Query: "insert into et values (0);",
-				Expected: []sql.Row{
-					{types.NewOkResult(1)},
-				},
+				Query:          "insert into et values (0);",
+				ExpectedErrStr: "Data truncated for column 'e' at row 1",
 			},
 		},
 	},

sql/types/enum.go

@@ -166,11 +166,9 @@ func (t EnumType) Convert(ctx context.Context, v interface{}) (interface{}, sql.
 	switch value := v.(type) {
 	case int:
 		// Check for 0 value in strict mode - MySQL behavior
+		// MySQL rejects 0 values in strict mode regardless of enum definition
 		if value == 0 && t.isStrictMode(ctx) {
-			// Check if empty string is explicitly defined as a valid enum value
-			if t.IndexOf("") == -1 {
-				return nil, sql.OutOfRange, ErrDataTruncatedForColumn.New("(unknown)")
-			}
+			return nil, sql.OutOfRange, ErrDataTruncatedForColumn.New("(unknown)")
 		}
 		if _, ok := t.At(value); ok {
 			return uint16(value), sql.InRange, nil