Merge pull request #8350 from waleed-elmelegy-arm/fix-null-dereference-in-x509-cert-write

Fix possible NULL dereference issue in X509 cert_write program

programs/x509/cert_write.c

@@ -583,6 +583,10 @@ usage:
 
                 if ((subtype_value = strchr(q, ':')) != NULL) {
                     *subtype_value++ = '\0';
+                } else {
+                    mbedtls_printf(
+                        "Invalid argument for option SAN: Entry must be of the form TYPE:value\n");
+                    goto usage;
                 }
                 if (strcmp(q, "RFC822") == 0) {
                     cur->node.type = MBEDTLS_X509_SAN_RFC822_NAME;