Fix passing null to strpos in gatherpress transformer (#69)

Reviewed-on: Event-Federation/wordpress-activitypub-event-bridge#69
Co-authored-by: André Menrath <andre.menrath@posteo.de>
Co-committed-by: André Menrath <andre.menrath@posteo.de>

composer.json

@@ -58,7 +58,7 @@
         ],
         "test-debug": [
             "@prepare-test",
-            "@test-modern-events-calendar-lite"
+            "@test-gatherpress"
         ],
         "test-vs-event-list": "phpunit --filter=vs_event_list",
         "test-the-events-calendar": "phpunit --filter=the_events_calendar",

includes/activitypub/transformer/class-gatherpress.php

@@ -124,7 +124,7 @@ final class GatherPress extends Event {
 	 */
 	public static function filter_gatherpress_blocks( $block_content, $block ) {
 		// Check if the block name starts with 'gatherpress'.
-		if ( strpos( $block['blockName'], 'gatherpress/' ) === 0 ) {
+		if ( isset( $block['blockName'] ) && 0 === strpos( $block['blockName'], 'gatherpress/' ) ) {
 			return ''; // Skip rendering this block.
 		}