Fix warning about sprintf() and NSTAT_HIST

The environment variable could contain format characters, causing
problems. Better to just use it directly.

misc/nstat.c

@@ -445,7 +445,7 @@ static void usage(void)
 
 int main(int argc, char *argv[])
 {
-	char hist_name[128];
+	char *hist_name;
 	struct sockaddr_un sun;
 	FILE *hist_fp = NULL;
 	int ch;
@@ -526,10 +526,10 @@ int main(int argc, char *argv[])
 	patterns = argv;
 	npatterns = argc;
 
-	if (getenv("NSTAT_HISTORY"))
-		snprintf(hist_name, sizeof(hist_name), getenv("NSTAT_HISTORY"));
-	else
+	if ((hist_name = getenv("NSTAT_HISTORY")) == NULL) {
+		hist_name = malloc(128);
 		sprintf(hist_name, "/tmp/.nstat.u%d", getuid());
+	}
 
 	if (reset_history)
 		unlink(hist_name);