Merge pull request #4871 from TD-er/bugfix/4870_empty_custom_build

[Build] Fix compile error when using default Custom.h (#4870)

Author: TD-er

src/src/Helpers/_CPlugin_init.cpp

@@ -2070,7 +2070,7 @@ const CPlugin_ptr_t PROGMEM CPlugin_ptr[] =
 constexpr size_t ProtocolIndex_to_CPlugin_id_size = sizeof(ProtocolIndex_to_CPlugin_id);
 
 // Highest CPlugin ID included in the build
-constexpr size_t Highest_CPlugin_id = ProtocolIndex_to_CPlugin_id[ProtocolIndex_to_CPlugin_id_size - 1];
+constexpr size_t Highest_CPlugin_id = ProtocolIndex_to_CPlugin_id_size == 0 ? 0 : ProtocolIndex_to_CPlugin_id[ProtocolIndex_to_CPlugin_id_size - 1];
 
 constexpr size_t CPlugin_id_to_ProtocolIndex_size = Highest_CPlugin_id + 1;