Prevent mcedit from hanging on macro

[jtyr]

Summary

Fixes editor hang when executing macro scripts via mc -e.

Problem

Running MC in editor-only mode (mc -e file) and executing a macro script (e.g., via edit_block_process_cmd) causes the editor to hang indefinitely.

The hang occurs in invoke_subshell() in src/subshell/common.c. Before sending a command to the subshell, the code sends Ctrl-C to clear any leftover input and calls feed_subshell(QUIETLY, FALSE) to wait for the shell to reach a prompt. This wait relies on the shell's prompt hook writing its CWD to a pipe - but in editor-only mode (MC_RUN_EDITOR), use_persistent_buffer is FALSE and the shell's CWD-reporting hook is not active, so feed_subshell blocks forever on select().

Fix

Skip the Ctrl-C + feed_subshell pre-clearing when not in full MC mode. This code path exists to clear user-typed text from the subshell prompt before injecting a command - but in editor mode, the subshell has not been interacted with by the user, so there is nothing to clear.

Test plan

• mc -e somefile - select a text block, run a macro script - should execute without hanging
• Full MC mode - run mc, edit a file (F4) and run a macro script - should work as before

[mc-worker]

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