tool: Fix 'idf.py bootloader' error if Secure Boot is enabled

If Secure Boot is enabled, there's no bootloader flasher arguments in the
project (to encourage careful manual flashing), so this command would
fail with a KeyError.

tools/idf.py

@@ -461,8 +461,6 @@ def init_cli(verbose_output=None):
             # Otherwise, if we built any binaries print a message about
             # how to flash them
             def print_flashing_message(title, key):
-                print("\n%s build complete. To flash, run this command:" % title)
-
                 with open(os.path.join(args.build_dir, "flasher_args.json")) as f:
                     flasher_args = json.load(f)
 
@@ -470,6 +468,10 @@ def init_cli(verbose_output=None):
                     return _safe_relpath(os.path.join(args.build_dir, f))
 
                 if key != "project":  # flashing a single item
+                    if key not in flasher_args:
+                        # This is the case for 'idf.py bootloader' if Secure Boot is on, need to follow manual flashing steps
+                        print("\n%s build complete." % title)
+                        return
                     cmd = ""
                     if (key == "bootloader"):  # bootloader needs --flash-mode, etc to be passed in
                         cmd = " ".join(flasher_args["write_flash_args"]) + " "
@@ -485,6 +487,8 @@ def init_cli(verbose_output=None):
                     for o, f in flash_items:
                         cmd += o + " " + flasher_path(f) + " "
 
+                print("\n%s build complete. To flash, run this command:" % title)
+
                 print(
                     "%s %s -p %s -b %s --before %s --after %s --chip %s %s write_flash %s" % (
                         PYTHON,