Fixed GSM encoded network initiated position request

GSM encoded network initiated position requests were previously
not correctly decoded. The GSM encoded string was decoded as
ASCII but not all characters are encoded in the same way for
GSM and ASCII. These characters was not displayed.

Besides that, when the number of characters was evenly divided
by 8 the last character was lost. This is also corrected.

Change-Id: Ic70b7c28bbba1f2936a9cc99e78f8002cc5c8761