check event color is initialized before using it

if we use the event color while its not initialized, the
color is still a valid color int (-1, white).
in this case we tried to find the uninitialized color
inside the available event colors and when the calendar
provided the white color, we used it erroneously
instead of the calendar color for new events.

fixes #1294

Change-Id: I60102f91c06a4b0552c1ea8ef5497d9f042878ec