detect-engine-analyzer: set EngineAnalysisCtx to NULL after free'ing

when engine-analysis is turned off in suricata.yaml
and we run suricata with --engine-analysis
suricata will try to use data from de_ctx->ea wich is
free'd in SetupEngineAnalysis() because fp_analysis and
rule_analysis is turned off and will receive SIGSEGV
with something like:
0x00007ffff7b4ac7b in _IO_new_fclose (fp=0xad96ab1cf5b38042) at ./libio/iofclose.c:48

Ticket: 8505

src/detect-engine-analyzer.c

@@ -506,6 +506,7 @@ void SetupEngineAnalysis(DetectEngineCtx *de_ctx, bool *fp_analysis, bool *rule_
         if (ea->analyzer_items)
             SCFree(ea->analyzer_items);
         SCFree(ea);
+        de_ctx->ea = NULL;
     }
 }