libselinux: getconlist: free memory on multiple level arguments

Do not leak memory if the program argument `l` got passed more than
once.

Found by clang-analyzer.

Signed-off-by: Christian Göttsche <cgzones@googlemail.com>

libselinux/utils/getconlist.c

@@ -26,6 +26,7 @@ int main(int argc, char **argv)
 	while ((opt = getopt(argc, argv, "l:")) > 0) {
 		switch (opt) {
 		case 'l':
+			free(level);
 			level = strdup(optarg);
 			if (!level) {
 				fprintf(stderr, "memory allocation failure: %d(%s)\n",