Ignore PLDM message if status objects not created

The OCC status objects are not created until after the host@0-on file
has been removed. This now delays when the objects are created.
This introduced a window where the host notified occ-control that the
OCCs were running (via PLDM) before the status objects were created
which led to a segfault.
This commit will verify the status object exists when getting the PLDM
callback.

Verified on Rainier

Change-Id: I72404d1b5d89c5259cc9f857c8087096644ef318
Signed-off-by: Chris Cain <cjcain@us.ibm.com>
diff --git a/occ_sensor.mako.hpp b/occ_sensor.mako.hpp
index 19c785f..123babb 100755
--- a/occ_sensor.mako.hpp
+++ b/occ_sensor.mako.hpp
@@ -14,7 +14,7 @@
 namespace occ
 {
 
-using instanceID = int;
+using instanceID = unsigned int;
 using sensorID = uint8_t;
 using sensorName = std::string;
 using sensorDefs = std::tuple<sensorID, sensorName>;