Fix potential increment past end in ethernet

Coverity warns that this is a bug.  GCC-15 treats it as a hard error.
Incrementing past the end of an iterator is undefined behavior, so add a
check to ensure it never happens.

This was originally submitted as part of a larger change here:
https://gerrit.openbmc.org/c/openbmc/bmcweb/+/81720

But because this is now breaking the build, put this in its own commit.

Tested: Not great testing available for this, and Redfish array behavior
is very subtle.  Inspection only.

Change-Id: I15669bb7212fbd330cf1022670c9ad558ffabe73
Signed-off-by: Ed Tanous <etanous@nvidia.com>
diff --git a/redfish-core/lib/ethernet.hpp b/redfish-core/lib/ethernet.hpp
index 1031e3d..53e21c5 100644
--- a/redfish-core/lib/ethernet.hpp
+++ b/redfish-core/lib/ethernet.hpp
@@ -1661,8 +1661,11 @@
                 lastGatewayPath = pathString;
             }
         }
-        nicIpEntry++;
-        nicIpEntry = getNextStaticIpEntry(nicIpEntry, ipv4Data.cend());
+        if (nicIpEntry != ipv4Data.end())
+        {
+            nicIpEntry++;
+            nicIpEntry = getNextStaticIpEntry(nicIpEntry, ipv4Data.cend());
+        }
         entryIdx++;
     }