[GPU] Move event completion wait to first of execute_impl (#23363)

### Details:
 - Move event completion wait to first of execute_impl

### Tickets:
 - 129373

src/plugins/intel_gpu/src/graph/impls/common/loop.cpp

@@ -167,6 +167,9 @@ struct loop_impl : typed_primitive_impl<loop> {
         // read initial execution condition from outer network
         int64_t execution_condition = 1;
         if (!primitive->first_execution_condition_id.empty()) {
+            // Wait for completion of the execution_condition of outer_network
+            if (outer_network.has_event(primitive->first_execution_condition_id))
+                outer_network.get_primitive_event(primitive->first_execution_condition_id)->wait();
             memory::ptr first_execution_condition_mem = outer_network.get_primitive(primitive->first_execution_condition_id)->output_memory_ptr();
             execution_condition = read_scalar_value(first_execution_condition_mem, stream);
         }