Bugfix: ISP Programmer and SubGhz (#2574)

* AVR_ISP: fix NULL pointer dereference
* SubGhz: double back with a blocked transmission in this region
* SubGhz: fix speaker, when a transmission is blocked in this region
* SubGhz: fix speaker
* SubGhz: return region
* AVR Flasher: cleanup code

Co-authored-by: Aleksandr Kutuzov <alleteam@gmail.com>

applications/external/avr_isp_programmer/helpers/avr_isp.c

@@ -152,7 +152,12 @@ bool avr_isp_auto_set_spi_speed_start_pmode(AvrIsp* instance) {
             }
         }
     }
-    if(instance->spi) avr_isp_spi_sw_free(instance->spi);
+
+    if(instance->spi) {
+        avr_isp_spi_sw_free(instance->spi);
+        instance->spi = NULL;
+    }
+
     return false;
 }