Fix BIFF8 DIMENSIONS record to use 0-based column indices

The XLS writer incorrectly used 1-based column indices in the BIFF8
DIMENSIONS record, violating the Microsoft Excel Binary File Format
specification which requires 0-based indices.

This bug caused an extra empty column to appear when converting XLS
files to other formats (e.g., CSV).

Changes:
- Modified column index initialization to subtract 1 from the result
  of Coordinate::columnIndexFromString() to convert from 1-based to
  0-based indexing
- Updated COLINFO loop to use the corrected 0-based lastColumnIndex

Per BIFF8 specification:
- colMic (first column) must be 0-based
- colMac (column after last column) must be 0-based

Example: For columns A-G (7 columns):
- Before: colMic=1, colMac=8 (incorrect)
- After:  colMic=0, colMac=7 (correct)

Fixes #4682

Author: zlatanovic-nebojsa

src/PhpSpreadsheet/Writer/Xls/Worksheet.php

@@ -214,8 +214,9 @@ public function __construct(int &$str_total, int &$str_unique, array &$str_table
         $this->firstRowIndex = $minR;
         $this->lastRowIndex = ($maxR > 65535) ? 65535 : $maxR;
 
-        $this->firstColumnIndex = Coordinate::columnIndexFromString($minC);
-        $this->lastColumnIndex = Coordinate::columnIndexFromString($maxC);
+        // BIFF8 requires 0-based column indices, but columnIndexFromString() returns 1-based
+        $this->firstColumnIndex = Coordinate::columnIndexFromString($minC) - 1;
+        $this->lastColumnIndex = Coordinate::columnIndexFromString($maxC) - 1;
 
         if ($this->lastColumnIndex > 255) {
             $this->lastColumnIndex = 255;
@@ -258,7 +259,8 @@ public function close(): void
         }
 
         $columnDimensions = $phpSheet->getColumnDimensions();
-        $maxCol = $this->lastColumnIndex - 1;
+        // lastColumnIndex is now 0-based, so no need to subtract 1
+        $maxCol = $this->lastColumnIndex;
         for ($i = 0; $i <= $maxCol; ++$i) {
             $hidden = 0;
             $level = 0;