AppLoader exception when no actual application is present

[LeZerb]

When reading OTA service Application Version with no application currently flashed AppLoader gets stuck.

This is caused by trying to read from an invalid address in bootload_checkApplicationPropertiesMagic and can be resolved by checking that the appProperties pointer is inside the actual flash area.

#if (FLASH_BASE > 0x0UL)
  if ((uint32_t)appProperties < FLASH_BASE) {
    return false;
  }
#endif

+  if ((uint32_t)appProperties > (FLASH_BASE + FLASH_SIZE - 16)) {
+    return false;
+  }