detect-engine-analyzer: remove unnecessary check

Always make sure, that smd is not NULL, as we dereference it a few
lines below and base64_data for instance is forbidden as a fast_pattern

Ticket: 8504

src/detect-engine-analyzer.c

@@ -1490,7 +1490,8 @@ void EngineAnalysisRules2(const DetectEngineCtx *de_ctx, const Signature *s)
         SCJbSetString(ctx.js, "buffer", name);
 
         SigMatchData *smd = pkt_mpm ? pkt_mpm->smd : app_mpm->smd;
-        if (smd == NULL && mpm_list == DETECT_SM_LIST_PMATCH) {
+        if (smd == NULL) {
+            DEBUG_VALIDATE_BUG_ON(mpm_list != DETECT_SM_LIST_PMATCH);
             smd = s->sm_arrays[mpm_list];
         }
         do {