In "Write Firmware", as long as a valid file was selected once, canceling then selecting an invalid file would pass the valididty check.

Fixes it, but not sure why it is required as we're supposed to overwrite the buffer each time we load a file for flashing - there might be a better fix.

radio/src/bootloader/boot.cpp

@@ -664,6 +664,7 @@ int main()
           // Select file to flash
           state = ST_FLASH_CHECK;
           Valid = 0;
+          memset(Block_buffer, 0, sizeof(Block_buffer));
         }
         else if (event == EVT_KEY_FIRST(BOOT_KEY_EXIT)) {
           state = ST_START;