Bug fix, motivated by issue #11

Although the n_last_peak_interval variable (the one that determines calculated heart rate) was properly initialized to the INIT_INTERVAL parameter, the first failure of the rf_signal_periodicity() routine was resetting it back to the FS value (a remnant of older code). For this reason, changing TYPICAL_HR to any other value than the 60 bpm default might have not resulted in desired effect.

algorithm_by_RF.cpp

@@ -98,7 +98,7 @@ void rf_heart_rate_and_oxygen_saturation(uint32_t *pun_ir_buffer, int32_t n_ir_b
     *pn_heart_rate = (int32_t)(FS60/n_last_peak_interval);
     *pch_hr_valid  = 1;
   } else {
-    n_last_peak_interval=FS;
+    n_last_peak_interval=INIT_INTERVAL;
     *pn_heart_rate = -999; // unable to calculate because signal looks aperiodic
     *pch_hr_valid  = 0;
     *pn_spo2 =  -999 ; // do not use SPO2 from this corrupt signal