AP_RCProtocol: fixed SBUS failsafe

thanks to Nate for spotting this

libraries/AP_RCProtocol/AP_RCProtocol.cpp

@@ -74,13 +74,14 @@ void AP_RCProtocol::process_pulse(uint32_t width_s0, uint32_t width_s1)
         }
         if (backend[i] != nullptr) {
             uint32_t frame_count = backend[i]->get_rc_frame_count();
+            uint32_t input_count = backend[i]->get_rc_input_count();
             backend[i]->process_pulse(width_s0, width_s1);
             if (frame_count != backend[i]->get_rc_frame_count()) {
                 _good_frames[i]++;
                 if (requires_3_frames((rcprotocol_t)i) && _good_frames[i] < 3) {
                     continue;
                 }
-                _new_input = true;
+                _new_input = (input_count != backend[i]->get_rc_input_count());
                 _detected_protocol = (enum AP_RCProtocol::rcprotocol_t)i;
                 memset(_good_frames, 0, sizeof(_good_frames));
                 _last_input_ms = now;
@@ -136,13 +137,14 @@ void AP_RCProtocol::process_byte(uint8_t byte, uint32_t baudrate)
     for (uint8_t i = 0; i < AP_RCProtocol::NONE; i++) {
         if (backend[i] != nullptr) {
             uint32_t frame_count = backend[i]->get_rc_frame_count();
+            uint32_t input_count = backend[i]->get_rc_input_count();
             backend[i]->process_byte(byte, baudrate);
             if (frame_count != backend[i]->get_rc_frame_count()) {
                 _good_frames[i]++;
                 if (requires_3_frames((rcprotocol_t)i) && _good_frames[i] < 3) {
                     continue;
                 }
-                _new_input = true;
+                _new_input = (input_count != backend[i]->get_rc_input_count());
                 _detected_protocol = (enum AP_RCProtocol::rcprotocol_t)i;
                 memset(_good_frames, 0, sizeof(_good_frames));
                 _last_input_ms = now;

libraries/AP_RCProtocol/AP_RCProtocol_Backend.h

@@ -46,6 +46,11 @@ public:
         return rc_frame_count;
     }
 
+    // get number of frames, honoring failsafe
+    uint32_t get_rc_input_count(void) const {
+        return rc_input_count;
+    }
+    
 protected:
     void add_input(uint8_t num_channels, uint16_t *values, bool in_failsafe);
 

libraries/AP_RCProtocol/AP_RCProtocol_SBUS.cpp

@@ -241,7 +241,7 @@ void AP_RCProtocol_SBUS::_process_byte(uint32_t timestamp_us, uint8_t b)
         if (sbus_decode(byte_input.buf, values, &num_values,
                         &sbus_failsafe, &sbus_frame_drop, SBUS_INPUT_CHANNELS) &&
             num_values >= MIN_RCIN_CHANNELS) {
-            add_input(num_values, values, false);
+            add_input(num_values, values, sbus_failsafe);
         }
         byte_input.ofs = 0;
     }