fix: Do not append SHA256 when --ram-only-header

When called with `--ram-only-header`, the ROM segments are hidden.
In this case, the end of the first two visible segments (in RAM)
is not the end of the image and is not suitable for appending the
SHA256 digest.

esptool/__init__.py

@@ -496,7 +496,7 @@ def main(argv=None, esp=None):
         "quantity. This will make the other segments invisible to the ROM "
         "loader. Use this argument with care because the ROM loader will load "
         "only the RAM segments although the other segments being present in "
-        "the output.",
+        "the output. Implies --dont-append-digest",
         action="store_true",
         default=None,
     )

esptool/cmds.py

@@ -1050,7 +1050,10 @@ def elf2image(args):
         image.min_rev_full = args.min_rev_full
         image.max_rev_full = args.max_rev_full
         image.ram_only_header = args.ram_only_header
-        image.append_digest = args.append_digest
+        if image.ram_only_header:
+            image.append_digest = False
+        else:
+            image.append_digest = args.append_digest
     elif args.version == "1":  # ESP8266
         image = ESP8266ROMFirmwareImage()
     elif args.version == "2":
@@ -1075,7 +1078,10 @@ def elf2image(args):
         image.elf_sha256_offset = args.elf_sha256_offset
 
     if args.ram_only_header:
-        print("ROM segments hidden - only RAM segments are visible to the ROM loader!")
+        print(
+            "Image has only RAM segments visible. "
+            "ROM segments are hidden and SHA256 digest is not appended."
+        )
         image.sort_segments()
 
     before = len(image.segments)