fix(dedent): stop removing spaces within non-indented lines

[Yanhu007]

Fixes #72

Problem

dedent.String incorrectly removes spaces from within lines that have less indentation than the minimum:

input := "This is an example\n\n  with no shared indent."
dedent.String(input)
// Output: "Thisisan example\n\nwith no shared indent."
//          ^^^^^^^^ spaces between words removed!

Root Cause

The dedent function sets shouldOmit = false only in the space/tab case (after omitting enough), but not in the default case. So after encountering the first non-whitespace character, shouldOmit remains true, and subsequent spaces in the same line are counted toward the omit quota.

Fix

Set shouldOmit = false in the default case, so that only leading whitespace is eligible for removal.

// After fix:
"This is an example\n\n  with no shared indent."
→ "This is an example\n\nwith no shared indent."
//  ✅ spaces within words preserved

All existing tests pass.