Fix up event source ids type: gint -> guint.

Fix up event source ids type: gint -> guint.
Functions like g_timeout_add() or g_idle_add() return a guint
greater than 0, but in most places it was wrongly stored as int
and initialized to -1.
This broke assertions matching in g_source_remove() for example
since id was always greater than 0 even when timer was not set
(-1 was casted to the biggest guint).