fix(textarea): prevent infinite loop in wordLeft on empty/start-of-text input

[djedi-knight]

Suggested PR

Title: fix(textarea): prevent infinite loop in wordLeft on empty/start-of-text input

Description:

Summary

textarea's word-backward motion (alt+left / alt+b) could spin forever and freeze the event loop when the textarea was empty or the cursor was already at the start of the text.

wordLeft() used an unconditional for {} that only exits once it finds a non-space rune:

for {
    m.characterLeft(true /* insideLine */)
    if m.col < len(m.value[m.row]) && !unicode.IsSpace(m.value[m.row][m.col]) {
        break
    }
}

When the textarea is empty (m.value == [][]rune{{}}, cursor at row=0, col=0), characterLeft(true) is a no-op and the break condition m.col < len(m.value[m.row]) evaluates to 0 < 0 == false. The loop never terminates, hanging the program.

Fix

Add a start-of-text guard at the top of the loop, mirroring the end-of-text break that doWordRight() already has. Since characterLeft always makes progress (moving up a row and/or left a column) until it reaches row 0, col 0, returning at that point guarantees termination and makes the motion a no-op on empty input.

for {
    if m.row == 0 && m.col == 0 {
        // Start of text.
        return
    }
    m.characterLeft(true /* insideLine */)
    ...
}

Related helpers audited

• deleteWordLeft / deleteWordRight — already guard m.col == 0 / len(m.value[m.row]) == 0; safe.
• doWordRight (and its callers wordRight, uppercaseRight, lowercaseRight, capitalizeRight, deleteWordRight) — already break at end of text; safe.
• wordLeft was the only word-motion helper missing the boundary guard.

Testing

Added TestWordBackwardEmptyTextareaTerminates, which drives an empty textarea with alt+left and alt+b. The update runs on a goroutine guarded by a 2s timeout, so a regression fails the test rather than hanging the suite, and asserts the motion is a no-op (cursor stays at row 0, col 0, value stays empty).

Verified the test fails against the unpatched code (times out) and passes with the fix. go test ./..., go vet ./..., and gofmt -l . are all clean.

Fixes charmbracelet/bubbletea#1652