Inspired idea to change TX standby code

Realised that data would be lost if dropping to standby or power down
mode before the FIFO is empty.
txStandby now returns a boolean value to indicate whether the
transmission is complete. If there is data in the TX FIFO the radio will
not drop out of TX mode. eg: while(  !txStandBy()  ){}

RF24.cpp

@@ -545,8 +545,13 @@ void RF24::startWrite( const void* buf, uint8_t len ){ //TMRh20
 }
 
 
-void RF24::txStandBy(){
+bool RF24::txStandBy(){
+
+	if ( (read_register(FIFO_STATUS) & _BV(TX_EMPTY))){
 		ce(LOW);
+		return 1;
+	}
+	return 0;
 }
 
 /****************************************************************************/

RF24.h

@@ -222,7 +222,7 @@ protected:
 public:
 
 //TMRh20
-	void txStandBy();
+	bool txStandBy();
 	bool writeBlocking( const void* buf, uint8_t len );
 	void reUseTX();
     bool writeFast( const void* buf, uint8_t len ); //Fills FIFO buffer, uses packet re-use function of the chip and returns 0 if packet failed and re-sent