Fix code scanning alert - Incorrect return-value check for a 'scanf'-like function

[gsnw]

Tracking issue for:

• [x] https://github.com/schweikert/fping/security/code-scanning/7
• [x] https://github.com/schweikert/fping/security/code-scanning/6
• [x] https://github.com/schweikert/fping/security/code-scanning/5
• [x] https://github.com/schweikert/fping/security/code-scanning/4
• [x] https://github.com/schweikert/fping/security/code-scanning/3
• [x] https://github.com/schweikert/fping/security/code-scanning/2
• [x] https://github.com/schweikert/fping/security/code-scanning/1

[gsnw]

Fix with pull-request #323