detect/content: don't leak replace memory

Replace keyword updates a prior content with a heap allocation of the
pattern the content should be replaced with. Make sure this is freed as
well.

Bug: #7997.

src/detect-content.c

@@ -379,6 +379,8 @@ void DetectContentFree(DetectEngineCtx *de_ctx, void *ptr)
     if (cd == NULL)
         SCReturn;
 
+    if (cd->replace)
+        SCFree(cd->replace);
     SpmDestroyCtx(cd->spm_ctx);
 
     SCFree(cd);