Fix zoom scale problems on reading bad xlsx files

Some computer programs will output xlsx files that do not compare 100%
to the standards. Excel will open the file without any problem.

setZoomScaleNormal() should throw exception when manually setting the
scale to less than or equals 0, but when reading files, we should
be able to read a file with such error, as Excel does.

Closes #350

CHANGELOG.md

@@ -10,6 +10,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 ### Added
 
 - HTML writer creates a generator meta tag - [#312](https://github.com/PHPOffice/PhpSpreadsheet/issues/312) 
+- Support invalid zoom value in XLSX format - [#350](https://github.com/PHPOffice/PhpSpreadsheet/pull/350)
 
 ### Fixed
 

src/PhpSpreadsheet/Reader/Xlsx.php

@@ -702,10 +702,24 @@ public function load($pFilename)
 
                             if (isset($xmlSheet->sheetViews, $xmlSheet->sheetViews->sheetView)) {
                                 if (isset($xmlSheet->sheetViews->sheetView['zoomScale'])) {
-                                    $docSheet->getSheetView()->setZoomScale((int) ($xmlSheet->sheetViews->sheetView['zoomScale']));
+                                    $zoomScale = (int) ($xmlSheet->sheetViews->sheetView['zoomScale']);
+                                    if ($zoomScale <= 0) {
+                                        // setZoomScale will throw an Exception if the scale is less than or equals 0
+                                        // that is OK when manually creating documents, but we should be able to read all documents
+                                        $zoomScale = 100;
+                                    }
+
+                                    $docSheet->getSheetView()->setZoomScale($zoomScale);
                                 }
                                 if (isset($xmlSheet->sheetViews->sheetView['zoomScaleNormal'])) {
-                                    $docSheet->getSheetView()->setZoomScaleNormal((int) ($xmlSheet->sheetViews->sheetView['zoomScaleNormal']));
+                                    $zoomScaleNormal = (int) ($xmlSheet->sheetViews->sheetView['zoomScaleNormal']);
+                                    if ($zoomScaleNormal <= 0) {
+                                        // setZoomScaleNormal will throw an Exception if the scale is less than or equals 0
+                                        // that is OK when manually creating documents, but we should be able to read all documents
+                                        $zoomScaleNormal = 100;
+                                    }
+
+                                    $docSheet->getSheetView()->setZoomScaleNormal($zoomScaleNormal);
                                 }
                                 if (isset($xmlSheet->sheetViews->sheetView['view'])) {
                                     $docSheet->getSheetView()->setView((string) $xmlSheet->sheetViews->sheetView['view']);