fix: pad short rows in SetRows to the number of columns

SetRows stored rows with fewer cells than the header unchanged, so short
rows rendered fmt's %!s(MISSING) verb and an empty row combined with a
first-column formatter panicked on vals[0]. Pad short rows to the column
count, mirroring AddRow's documented behavior of rendering missing cells
as empty.

table.go

@@ -238,10 +238,13 @@ func (t *table) SetRows(rows [][]string) Table {
 	headerLength := len(t.header)
 
 	for _, row := range rows {
-		if len(row) > headerLength {
+		if len(row) >= headerLength {
 			t.rows = append(t.rows, row[:headerLength])
 		} else {
-			t.rows = append(t.rows, row)
+			// pad short rows so every column is rendered, matching AddRow
+			padded := make([]string, headerLength)
+			copy(padded, row)
+			t.rows = append(t.rows, padded)
 		}
 	}