detect/flowvar: remove extra NULL check

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

src/detect-flowvar.c

@@ -192,7 +192,6 @@ static int DetectFlowvarSetup (DetectEngineCtx *de_ctx, Signature *s, const char
     return 0;
 
 error:
-    if (fd != NULL)
     DetectFlowvarDataFree(de_ctx, fd);
     if (content != NULL)
         SCFree(content);
@@ -272,7 +271,6 @@ int DetectFlowvarPostMatchSetup(DetectEngineCtx *de_ctx, Signature *s, uint32_t
     }
     return 0;
 error:
-    if (fv != NULL)
     DetectFlowvarDataFree(de_ctx, fv);
     return -1;
 }