Merge pull request #413 from bsekisser/sim_regbit_clear_check_valid_reg

Remove kludge "avr_uart_regbit_clear" from uart

diff --cc simavr/sim/avr_uart.c
Simple merge

diff --cc simavr/sim/sim_regbit.h
index 76f4f5e,4b511e9..10ecc56
--- 1/simavr/sim/sim_regbit.h
--- 2/simavr/sim/sim_regbit.h
+++ b/simavr/sim/sim_regbit.h
@@@ -134,12 -116,11 +134,14 @@@ avr_regbit_get_raw
        return (avr->data[a]) & (rb.mask << rb.bit);
  }
  
 -static inline uint8_t avr_regbit_clear(avr_t * avr, avr_regbit_t rb)
 +static inline uint8_t
 +avr_regbit_clear(
 +      avr_t * avr,
 +      avr_regbit_t rb)
  {
        uint16_t a = rb.reg;
+       if (!a)
+               return 0;
        uint8_t m = rb.mask << rb.bit;
        avr_core_watch_write(avr, a, avr->data[a] & ~m);
        return avr->data[a];