[MM-61459] Fix errcheck issues in server/channels/app/plugin_signatur… (#29202)

server/.golangci.yml

@@ -118,7 +118,6 @@ issues:
         channels/app/platform/web_hub.go|\
         channels/app/platform/web_hub_test.go|\
         channels/app/plugin_install.go|\
-        channels/app/plugin_signature.go|\
         channels/app/plugin_signature_test.go|\
         channels/app/plugin_test.go|\
         channels/app/post.go|\

server/channels/app/plugin_signature.go

@@ -90,8 +90,14 @@ func (ch *Channels) verifyPlugin(plugin, signature io.ReadSeeker) *model.AppErro
 			continue
 		}
 		publicKey := bytes.NewReader(pkBytes)
-		plugin.Seek(0, 0)
-		signature.Seek(0, 0)
+		if _, err := plugin.Seek(0, io.SeekStart); err != nil {
+			mlog.Warn("Unable to seek in public key reader for ", mlog.String("filename", pk))
+			continue
+		}
+		if _, err := signature.Seek(0, io.SeekStart); err != nil {
+			mlog.Warn("Unable to seek in signature for public key ", mlog.String("filename", pk))
+			continue
+		}
 		if err := verifySignature(publicKey, plugin, signature); err == nil {
 			return nil
 		}