x11: Set icon issue fix

Signed-off-by: Vinzenz Feenstra <evilissimo@gmail.com>
Addressed comments by Terseus to match the spec

size_t -> long
uint8_t -> unsigned char

Signed-off-by: Vinzenz Feenstra <evilissimo@gmail.com>
Merge pull request #69 from vinzenz/icon-issue

x11: Set icon issue fix