Added else clause

If checksum wasn't there, parser was parsing anyways. If checksum is required we need to return false if not found.

Adafruit_GPS.cpp

@@ -46,6 +46,8 @@ boolean Adafruit_GPS::parse(char *nmea) {
       // bad checksum :(
       return false;
     }
+  } else {
+  	return false;
   }
   int32_t degree;
   long minutes;