rbus: fixup reverse null check in rtMessage_Retain_test1

[svc-rdkeportal01]

Fix REVERSE_INULL in rtMessage_Retain_test1

Issues Fixed

• Coverity CID 139: REVERSE_INULL in unittests/rbus_unit_test_server.cpp at line 1320

Root Cause

The code was checking if msg is NULL after already dereferencing it in rtMessage_Retain(msg). This is a logic error - if msg was NULL, the code would crash at line 1317 before reaching the NULL check at line 1320.

Changes Made

Removed redundant NULL check:

Before:

rtMessage_Create(&msg);
err = rtMessage_Retain(msg);  // Line 1317: Dereferences msg
EXPECT_EQ(err, RT_OK);
rtMessage_Release(msg);
if(msg)  // Line 1320: Checks NULL (too late!)
   rtMessage_Release(msg);

After:

rtMessage_Create(&msg);
err = rtMessage_Retain(msg);
EXPECT_EQ(err, RT_OK);
rtMessage_Release(msg);
rtMessage_Release(msg);  // No redundant check needed

Why This Fix is Correct

• rtMessage_Create() guarantees msg is non-NULL
• If msg was NULL, the test would fail at EXPECT_EQ(err, RT_OK)
• The NULL check at line 1320 was redundant and misleading
• Second rtMessage_Release() is intentional (testing double release behavior)