[chore][fileconsumer] Cleanup file handle when closed by reader (#25912)

This PR is a small step towards reducing complexity in the way we manage
readers and their files. With this change we now have an expectation
that reader file handles are always open.

pkg/stanza/fileconsumer/file.go

@@ -157,10 +157,7 @@ func (m *Manager) consume(ctx context.Context, paths []string) {
 			r.ReadToEnd(ctx)
 			// Delete a file if deleteAfterRead is enabled and we reached the end of the file
 			if m.deleteAfterRead && r.eof {
-				r.Close()
-				if err := os.Remove(r.file.Name()); err != nil {
-					m.Errorf("could not delete %s", r.file.Name())
-				}
+				r.Delete()
 			}
 		}(r)
 	}

pkg/stanza/fileconsumer/reader.go

@@ -124,12 +124,25 @@ func (r *reader) finalizeHeader() {
 	r.HeaderFinalized = true
 }
 
+// Delete will close and delete the file
+func (r *reader) Delete() {
+	if r.file == nil {
+		return
+	}
+	f := r.file
+	r.Close()
+	if err := os.Remove(f.Name()); err != nil {
+		r.Errorf("could not delete %s", f.Name())
+	}
+}
+
 // Close will close the file
 func (r *reader) Close() {
 	if r.file != nil {
 		if err := r.file.Close(); err != nil {
 			r.Debugw("Problem closing reader", zap.Error(err))
 		}
+		r.file = nil
 	}
 
 	if r.headerReader != nil {