avoid memory corruption when calling RF24::read(0) on linux machines

Signed-off-by: mz-fuzzy <mzfuzzy800@gmail.com>

RF24.cpp

@@ -290,10 +290,12 @@ uint8_t RF24::read_payload(void* buf, uint8_t data_len)
 	
 	status = *prx++; // 1st byte is status	
     
+    if (data_len > 0) {
       while ( --data_len ) // Decrement before to skip 1st status byte
           *current++ = *prx++;
 		
       *current = *prx;
+    }
 	endTransaction();
   #else