Splash screen file name casing not checked

[DanyiLin]

Provide a splash screen name that has wrong casing. e.g., img/z10_splash.png instead of img/Z10_splash.png

• Actual Result: Name is accepted on configuration screen, but causes error when you try to build on build screen
• Expected Result: Name would be rejected on the configuration screen
• Workaround: Use correct casing on the file name