Fixed errcheck issues in server/channels/app/plugin_install.go (#29062)

Co-authored-by: Ben Schumacher <ben.schumacher@mattermost.com>

server/.golangci.yml

@@ -115,7 +115,6 @@ issues:
         channels/app/platform/web_conn.go|\
         channels/app/platform/web_hub.go|\
         channels/app/platform/web_hub_test.go|\
-        channels/app/plugin_install.go|\
         channels/app/plugin_signature_test.go|\
         channels/app/plugin_test.go|\
         channels/app/post_helpers_test.go|\

server/channels/app/plugin_install.go

@@ -389,7 +389,9 @@ func (ch *Channels) installPluginLocally(bundle io.ReadSeeker, installationStrat
 
 // extractPlugin unpacks the given plugin bundle into the specified directory.
 func extractPlugin(bundle io.ReadSeeker, extractDir string) (*model.Manifest, string, *model.AppError) {
-	bundle.Seek(0, 0)
+	if _, err := bundle.Seek(0, 0); err != nil {
+		return nil, "", model.NewAppError("extractPlugin", "app.plugin.seek.app_error", nil, "", http.StatusInternalServerError).Wrap(err)
+	}
 	if err := extractTarGz(bundle, extractDir); err != nil {
 		return nil, "", model.NewAppError("extractPlugin", "app.plugin.extract.app_error", nil, "", http.StatusBadRequest).Wrap(err)
 	}

server/i18n/en.json

@@ -6154,6 +6154,10 @@
     "id": "app.plugin.restart.app_error",
     "translation": "Unable to restart plugin on upgrade."
   },
+  {
+    "id": "app.plugin.seek.app_error",
+    "translation": "Unable to reset the read position to the start of the plugin bundle."
+  },
   {
     "id": "app.plugin.signature_decode.app_error",
     "translation": "Unable to decode base64 signature."