Bugfix inverted whitspace: In the print substring function white spaces are bypassed by just increasing the drawing position without really putting a pixel on the screen. As results white space were not draw as yellow boxes resulting in a bad inverted string visualization. => Changed implementation to not bypass inverted white spaces.

Imported from Ac6/SystemWorkbench/plugins/fr.ac6.mcu.firmware_1.14.7.201711101414/resources/builtin/:
* File syscalls.c