core: initialize fatfs only after we know the SD card is powered

core/src/apps/common/sd_salt.py

@@ -116,11 +116,12 @@ async def set_sd_salt(
     salt_path = "%s/%s" % (device_dir, filename)
 
     sd = io.SDCard()
-    fs = io.FatFS()
     if not sd.power(True):
         await insert_card_dialog(ctx)
         raise SdProtectCancelled
 
+    fs = io.FatFS()
+
     try:
         fs.mount()
         fs.mkdir("/trezor", True)

core/src/boot.py

@@ -75,8 +75,8 @@ async def lockscreen() -> None:
 if utils.EMULATOR:
     # Ensure the emulated SD card is FAT32 formatted.
     sd = io.SDCard()
-    fs = io.FatFS()
     sd.power(True)
+    fs = io.FatFS()
     try:
         fs.mount()
     except OSError: