fixed 12-year old bug in setMonitor that would make the try-finally d…

…esign pattern around setting one and restoring the old one break and return always to the latest one. This then breaks VScode and Eclipse terminal features such as implemented in util::IDEServices.

src/org/rascalmpl/interpreter/Evaluator.java

@@ -314,7 +314,7 @@ public IRascalMonitor setMonitor(IRascalMonitor monitor) {
         }
 
         interrupt = false;
-        IRascalMonitor old = monitor;
+        IRascalMonitor old = this.monitor;
         this.monitor = monitor;
         return old;
     }