requester: Fix error handling in registerRequest

Add error handling for pollEndpointQueue in registerRequest to
prevent incorrect PLDM_SUCCESS returns.
This ensures SendRecvMsgSender can handle send failures, preventing
discoverMctpTerminusTask from stalling and remaining incomplete.

Change-Id: I153934490ee848166e7dce5892136bbbdeeacdd9
Signed-off-by: Eric Yang <eric.yang.wiwynn@gmail.com>
diff --git a/requester/handler.hpp b/requester/handler.hpp
index 33d9cb9..3677243 100644
--- a/requester/handler.hpp
+++ b/requester/handler.hpp
@@ -287,7 +287,14 @@
         }
 
         /* try to send new request if the endpoint is free */
-        pollEndpointQueue(eid);
+        auto rc = pollEndpointQueue(eid);
+        if (rc != PLDM_SUCCESS)
+        {
+            error(
+                "Failed to process request queue for EID {EID}, response code {RC}.",
+                "EID", eid, "RC", rc);
+            return rc;
+        }
 
         return PLDM_SUCCESS;
     }