SCI: Fix angle rounding in the SCI1 implementation of kGetAngle (bug #3601479)

Fixes bug #3601479 - "SCI KQ6: Castle walls - stuck in same room".
Many thanks to wjp for his help on the kGetAngle implementation
SCI: Fix uninitialized variable workaround for scene 510 (bug #3575570)

A non-zero value must be used in the uninitialized variable, otherwise
the prize is awarded twice. Fixes bug #3575570 - "SCI: QfG3: Both the
player and Yesufu are declared winners"