fix: Use nullish coalescing over || op for channel_axis (#115)

Author: manzt

src/io.ts

@@ -159,7 +159,7 @@ export async function createSourceData(config: ImageLayerConfig): Promise<Source
   // If explicit channel axis is provided, try to load as multichannel.
   if ('channel_axis' in config || labels.includes('c')) {
     config = config as MultichannelConfig;
-    config.channel_axis = config.channel_axis || labels.indexOf('c');
+    config.channel_axis = config.channel_axis ?? labels.indexOf('c');
     return loadMultiChannel(config, loader, max);
   }