platform-mc: Fix null deref in initTerminus

Commit [1] changed initTerminus() to snapshot TIDs before iterating, but
the loop still looks up each terminus by TID using operator[]. If a
terminus is removed between iterations, operator[] silently inserts a
null entry instead of failing, causing a null pointer dereference on the
next access.

Add a contains() guard before the lookup so that removed TIDs are
skipped, consistent with the existing guards after each co_await.

Tested:
On a Yosemite 4 platform, repeated chassis power cycles trigger the
race. With the fix applied and a temporary log confirming the guard
fires, initTerminus completes without crash.

Reference:
[1] https://gerrit.openbmc.org/c/openbmc/pldm/+/89709

Change-Id: I948d78bfd6087ac2496489752a3291ce5f34eb68
Signed-off-by: Eric Yang <eric.yang.wiwynn@gmail.com>

platform-mc/platform_manager.cpp

diff --git a/platform-mc/platform_manager.cpp b/platform-mc/platform_manager.cpp
index 93ad701..b6c9d81 100644
--- a/platform-mc/platform_manager.cpp
+++ b/platform-mc/platform_manager.cpp
@@ -27,6 +27,13 @@
 
     for (const auto tid : tids)
     {
+        // termini[tid] would auto-insert if the TID was erased after the
+        // snapshot above.
+        if (!termini.contains(tid))
+        {
+            continue;
+        }
+
         /* Take a local shared_ptr copy so the Terminus object stays alive even
          * if the map entry is erased while this coroutine is suspended. */
         auto terminus = termini[tid];