[rilmodem] do not check spdi if mcc and mnc are not valid

It is possible that network is received before current operator
is retrieved. In rare occasions this causes crash when tried
to compare mnc and mcc of current operator to spdi.

Signed-off-by: Jussi Kangas <jussi.kangas@oss.tieto.com>
Merge pull request #113 from jkangas/master

Request for pulling mcc and mnc presence check before spdi search to main branch