detect/flowint: remove extra NULL check

The fn DetectFlowintFree checks if the pointer (DetectFlowintData)
passed to it is valid. So, the checks for NULL in the call sites can
safely be removed.

src/detect-flowint.c

@@ -354,8 +354,6 @@ error:
         pcre2_substring_free((PCRE2_UCHAR *)varval);
     if (modstr)
         pcre2_substring_free((PCRE2_UCHAR *)modstr);
-    if (sfd != NULL)
-        SCFree(sfd);
     return NULL;
 }
 
@@ -410,7 +408,6 @@ static int DetectFlowintSetup(DetectEngineCtx *de_ctx, Signature *s, const char
     return 0;
 
 error:
-    if (sfd)
     DetectFlowintFree(de_ctx, sfd);
     return -1;
 }