Handle plugin not found due to mixed plugin metadata

CURA-5202

Plugin metadata that comes from the plugin server is also saved into
PluginRegistry's metadata collection, so it's all mixed. Plugins that
are just installed cannot be loaded immediately, and this causes an
error in checkCanUpgrade().

plugins/PluginBrowser/PluginBrowser.py

@@ -6,6 +6,7 @@ from PyQt5.QtNetwork import QNetworkAccessManager, QNetworkRequest, QNetworkRepl
 
 from UM.Application import Application
 from UM.Logger import Logger
+from UM.PluginError import PluginNotFoundError
 from UM.PluginRegistry import PluginRegistry
 from UM.Qt.Bindings.PluginsModel import PluginsModel
 from UM.Extension import Extension
@@ -302,10 +303,15 @@ class PluginBrowser(QObject, Extension):
         return self._plugins_model
 
     def _checkCanUpgrade(self, plugin_id, version):
-        if plugin_id not in self._plugin_registry.getInstalledPlugins():
+        if not self._plugin_registry.isInstalledPlugin(plugin_id):
+            return False
+
+        try:
+            plugin_object = self._plugin_registry.getPluginObject(plugin_id)
+        except PluginNotFoundError:
+            Logger.log("w", "Could not find plugin %s", plugin_id)
             return False
 
-        plugin_object = self._plugin_registry.getPluginObject(plugin_id)
         # Scan plugin server data for plugin with the given id:
         for plugin in self._plugins_metadata:
             if plugin_id == plugin["id"]: