mkarchiso: do not pad the ISO when it is not necessary

If the ISO exceeds the max size of a CD (900 MiB), the 300 KiB padding
needed for CDs can be removed.

CHANGELOG.rst

@@ -17,6 +17,7 @@ Changed
 - Increase the additional free space of the EFI partition size from 1 MiB to 8 MiB to account for file system overhead
   when using FAT32 (needs less than 1 MiB) and to give more space for adding custom files when repacking an ISO (e.g.
   when preparing it for Secure Boot).
+- Remove 300 KiB padding needed for CDs if the ISO exceeds the maximum size of a CD.
 
 Deprecated
 ----------

archiso/mkarchiso

@@ -1735,6 +1735,11 @@ _build_iso_image() {
         typeset -f "_add_xorrisofs_options_${bootmode}" &>/dev/null && "_add_xorrisofs_options_${bootmode}"
     done
 
+    # Remove 300 KiB padding needed for CDs if the ISO exceeds the max size of a CD
+    if (( $(du -s --apparent-size -B1M "${isofs_dir}/" | awk '{ print $1 }') > 900 )); then
+        xorrisofs_options+=('-no-pad')
+    fi
+
     rm -f -- "${out_dir}/${image_name}"
     _msg_info "Creating ISO image..."
     xorriso "${xorriso_options[@]}" -as mkisofs \