Fix out-of-bounds string index warning

src/wp-includes/interactivity-api/class-wp-interactivity-api.php

@@ -576,7 +576,10 @@ private function data_wp_bind_processor( WP_Interactivity_API_Directives_Process
 				$attribute_value = $p->get_attribute( $attribute_name );
 				$result          = $this->evaluate( $attribute_value, end( $namespace_stack ), end( $context_stack ) );
 
-				if ( null !== $result && ( false !== $result || '-' === $bound_attribute[4] ) ) {
+				if ( null !== $result && (
+						false !== $result ||
+						( strlen( $bound_attribute ) > 5 && '-' === $bound_attribute[4] )
+				) ) {
 					/*
 					 * If the result of the evaluation is a boolean and the attribute is
 					 * `aria-` or `data-, convert it to a string "true" or "false". It