mmdbresolve: check the return value of malloc

The return value of malloc() is used without validation

Bug: 15851
Change-Id: I2635937d3107a75076e9bbee536797d97792683d
Reviewed-on: https://code.wireshark.org/review/33705
Petri-Dish: Anders Broman <a.broman58@gmail.com>
Tested-by: Petri Dish Buildbot
Reviewed-by: Anders Broman <a.broman58@gmail.com>

mmdbresolve.c

@@ -68,6 +68,10 @@ main(int argc, char *argv[])
     int mmdb_err;
 
     char *out_buf = (char *) malloc(OUT_BUF_SIZE);
+    if (out_buf == NULL) {
+        fprintf(stdout, "ERROR: malloc failed\n");
+        return 1;
+    }
     setvbuf(stdout, out_buf, _IOFBF, OUT_BUF_SIZE);
 
     fprintf(stdout, "[init]\n");