imgtool: fix "align" script error

Fix "align" possible script error, caused by mcu-tools#1833

Signed-off-by: Andrej Butok <[email protected]>

scripts/imgtool/main.py

@@ -416,7 +416,7 @@ def sign(key, public_key_format, align, version, pad_sig, header_size,
         pad = True
     img = image.Image(version=decode_version(version), header_size=header_size,
                       pad_header=pad_header, pad=pad, confirm=confirm,
-                      align=int(align), slot_size=slot_size,
+                      align = int(align) if align else 1, slot_size=slot_size,
                       max_sectors=max_sectors, overwrite_only=overwrite_only,
                       endian=endian, load_addr=load_addr, rom_fixed=rom_fixed,
                       erased_val=erased_val, save_enctlv=save_enctlv,