Ignore invalid GPS locations

Apparantly the GPS location fields can also contain the magic value
0xFFFFFFFF (or -1 as signed integer) to indicate the absence of a GPS
location.

Reported-by: Greg McLaughlin <[email protected]>

Author: jefdriesen

src/shearwater_predator_parser.c

@@ -1102,7 +1102,8 @@ shearwater_predator_parser_get_field (dc_parser_t *abstract, dc_field_type_t typ
 				return DC_STATUS_UNSUPPORTED;
 			latitude  = (signed int) array_uint32_be (data + parser->opening[9] + 21);
 			longitude = (signed int) array_uint32_be (data + parser->opening[9] + 25);
-			if (latitude == 0 && longitude == 0)
+			if ((latitude == 0 && longitude == 0) ||
+				(latitude == -1 && longitude == -1))
 				return DC_STATUS_UNSUPPORTED;
 			location->latitude  = latitude  / 100000.0;
 			location->longitude = longitude / 100000.0;