Throw parsing exception for non-date-time values in POV

src/main/java/caosdb/server/query/POV.java

@@ -167,6 +167,9 @@ public class POV implements EntityFilterInterface {
       } catch (final ClassCastException e) {
         this.vDatetime = null;
       } catch (final IllegalArgumentException e) {
+        if (this.operator.contains("(")) {
+          throw new Query.ParsingException("the value is expected to be a date time");
+        }
         this.vDatetime = null;
       }
     } else {