51.011: Fix EF_SST decoder for services > table description

Before:
EXCEPTION of type 'KeyError' occurred with message: '60'

After:
    "60": {
        "description": null,
        "allocated": false,
        "activated": false
    }

Change-Id: Ic089f9632a936bdbedd2344442678c5bf9797713

pySim/ts_51_011.py

@@ -513,7 +513,7 @@ class EF_ServiceTable(TransparentEF):
             bit_offset = (i % 4) * 2
             bits = (byte >> bit_offset) & 3
             ret[service_nr] = {
-                     'description': self.table[service_nr] or None,
+                     'description': self.table[service_nr] if service_nr in self.table else None,
                      'allocated': True if bits & 1 else False,
                      'activated': True if bits & 2 else False,
                      }