processor_content_modifier: skip GROUP_START markers during metadata/body processing

Skip GROUP_START markers when the processor is operating on log metadata
or body contexts. This prevents the processor from attempting to process
group markers as regular log records, which would cause errors since
group markers have a different structure than normal log events.

Signed-off-by: Eduardo Silva <eduardo@chronosphere.io>

Author: edsiper

plugins/processor_content_modifier/cm_logs.c

@@ -316,6 +316,12 @@ int cm_logs_process(struct flb_processor_instance *ins,
             continue;
         }
 
+        if (record_type == FLB_LOG_EVENT_GROUP_START &&
+            (ctx->context_type == CM_CONTEXT_LOG_METADATA ||
+             ctx->context_type == CM_CONTEXT_LOG_BODY)) {
+            continue;
+        }
+
         /* retrieve the target cfl object */
         if (ctx->context_type == CM_CONTEXT_LOG_METADATA) {
             obj = record->cobj_metadata;