refdb_fs: remove unnecessary check for NULL

The fail-label of `reflog_parse` explicitly checks the entry
poitner for NULL before freeing it. When we jump to the label the
variable has to be set to a non-NULL and valid pointer though: if
the allocation fails we immediately return with an error code and
if the loop was not entered we return with a success code,
withouth executing the label's code.

Remove the useless NULL-check to silence Coverity.

src/refdb_fs.c

@@ -1512,8 +1512,7 @@ static int reflog_parse(git_reflog *log, const char *buf, size_t buf_size)
 #undef seek_forward
 
 fail:
-	if (entry)
-		git_reflog_entry__free(entry);
+	git_reflog_entry__free(entry);
 
 	return -1;
 }