utils.py: raise error if rootfs file size is not multiple of 4KiB.

See: AOSC-Dev/aosc-asahi-installer@f46e12d,
if rootfs image size can not multipie of 4KiB, asahi-installer will raise `EINVAL`, users don't know whats happen ...

The point of this commit is to look for illegitimate rootfs image sizes in advance, so that the raise error becomes clear.

Signed-off-by: eatradish <[email protected]>

Author: eatradish

src/util.py

@@ -197,6 +197,8 @@ def extract(self, src, dest):
         self.extract_file(src, dest_path)
 
     def fdcopy(self, sfd, dfd, size=None):
+        if size is not None and size % (4 * 1024) != 0:
+            raise Exception("The size of the rootfs image file must be a multiple of 4KiB.")
         BLOCK = 16 * 1024 * 1024
         copied = 0
         bps = 0