perf: Do not index attachments after plugin has loaded (#2465)

Fixes #2464

Non-markdown files that were added, renamed or deleted after the plugin had loaded
were being passed to Cache.indexFile() which was then reading them.

This could cause wasted work, and when deleting non-markdown files,
would trigger Tasks search results to be needlessly redrawn.

src/Cache.ts

@@ -217,7 +217,8 @@ export class Cache {
         }
 
         if (!file.path.endsWith('.md')) {
-            this.logger.warn('indexFile: WARNING: indexing non-markdown file: ' + file.path);
+            this.logger.debug('indexFile: skipping non-markdown file: ' + file.path);
+            return;
         }
 
         this.logger.debug('Cache.indexFile: ' + file.path);