Allow LimitOperator in Driver assertion (elastic#130235) (elastic#130297)

The LimitOperator can be finished early because the Limiter may be
shared across operators. This PR relaxes the assertion to allow for
this.

Closes elastic#130228
Closes elastic#130219

(cherry picked from commit ddef899)

Author: dnhatn

x-pack/plugin/esql/compute/src/main/java/org/elasticsearch/compute/operator/Driver.java

@@ -292,6 +292,8 @@ private IsBlockedResult runSingleLoopIteration() {
 
             if (op.isFinished() == false && nextOp.needsInput()) {
                 driverContext.checkForEarlyTermination();
+                assert nextOp.isFinished() == false || nextOp instanceof ExchangeSinkOperator || nextOp instanceof LimitOperator
+                    : "next operator should not be finished yet: " + nextOp;
                 Page page = op.getOutput();
                 if (page == null) {
                     // No result, just move to the next iteration