Do not use optional chaining on a potentially undeclared root object

The global "OC" variable may be undefined depending on the
initialization order, so optional chaining ("OC?.config" and
"OC?.debug") was added to prevent accessing fields on an undefined
variable.

However, "OC" could be not only undefined, but also undeclared. Optional
chaining can not be used on an undeclared root object, so it needs to be
explicitly guarded against that to prevent a ReferenceError to be
thrown.

Signed-off-by: Daniel Calviño Sánchez <danxuliu@gmail.com>

lib/LoggerBuilder.ts

@@ -15,9 +15,9 @@ export class LoggerBuilder {
         this.context = {}
         this.factory = factory
         // Up to, including, nextcloud 24 the loglevel was not exposed
-        this.context.level = OC?.config?.loglevel !== undefined ? OC.config.loglevel : LogLevel.Warn
+        this.context.level = (window.hasOwnProperty('OC') && OC?.config?.loglevel !== undefined) ? OC.config.loglevel : LogLevel.Warn
         // Override loglevel if we are in debug mode
-        if (OC?.debug) {
+        if (window.hasOwnProperty('OC') && OC?.debug) {
             this.context.level = LogLevel.Debug
         }
     }