engine/analyzer: check if file pointer exists before writing

de_ctx->ea->fp_engine_analysis_fp is only initialized if
engine-analysis.rules-fast-pattern is enabled in the configuration. If
this config param is missing, this leads to segfault.

Bug 7822

src/detect-engine-analyzer.c

@@ -622,6 +622,7 @@ static void EngineAnalysisRulesPrintFP(const DetectEngineCtx *de_ctx, const Sign
 void EngineAnalysisRulesFailure(
         const DetectEngineCtx *de_ctx, const char *line, const char *file, int lineno)
 {
+    if (de_ctx->ea->fp_engine_analysis_fp) {
         fprintf(de_ctx->ea->fp_engine_analysis_fp, "== Sid: UNKNOWN ==\n");
         fprintf(de_ctx->ea->fp_engine_analysis_fp, "%s\n", line);
         fprintf(de_ctx->ea->fp_engine_analysis_fp, "    FAILURE: invalid rule.\n");
@@ -629,6 +630,7 @@ void EngineAnalysisRulesFailure(
         fprintf(de_ctx->ea->fp_engine_analysis_fp, "    Line: %d.\n", lineno);
         fprintf(de_ctx->ea->fp_engine_analysis_fp, "\n");
     }
+}
 
 typedef struct RuleAnalyzer {
     SCJsonBuilder *js; /* document root */