refactor(stats): drop redundant n_for_mapq conditional in PE caller

n_for_mapq is usize, so `if n > 0 { n } else { 0 }` is identical to
passing n_for_mapq directly to record_alignment. Match the SE caller
shape: the variable already carries the right count from the PE
TooManyLoci return site, and record_alignment routes via max_multimaps.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: pinin4fjords

src/lib.rs

@@ -1454,8 +1454,7 @@ fn align_reads_paired_end<W: AlignmentWriter + ?Sized>(
                     .collect();
 
                 if results.is_empty() {
-                    let n_for_stats = if n_for_mapq > 0 { n_for_mapq } else { 0 };
-                    stats.record_alignment(n_for_stats, max_multimaps);
+                    stats.record_alignment(n_for_mapq, max_multimaps);
                     stats.record_unmapped_reason(
                         unmapped_reason.unwrap_or(crate::stats::UnmappedReason::Other),
                     );