Improve Coverage for Gnumeric (#1517)

* Improve Coverage for Gnumeric

I believe that both BaseReader and Gnumeric Reader are now 100% covered.

My goal was to use PhpSpreadsheet to load the test file,
save it as Xlsx, and visually compare the two, then add a test
loaded with assertions. Results were generally pretty good,
but there were no tests with assertions. I added a few cells
to exercise some previously uncovered code. Code was extensively
refactored; logic changes are noted below.

Code allowed for specifying document properties in an old format.
I considered removing that, but I found the original spec at
http://www.jfree.org/jworkbook/download/gnumeric-xml.pdf
This allowed me to create an old file, which was not handled
correctly because of namespace differences. The code was corrected
to allow for this difference.

Added support for textRotation.

Mapping of fill types was not correct.

* PHP7.2 Error

One assertion failed under PHP7.2. Apparently there was some change in
the handling of SimpleXMLElement between 7.2 and 7.3. Casting to string
before use eliminates the problem.

* Scrutinizer Recommendations

All minor, solved (hopefully) mostly by casts.

* One Last Scrutinizer Fix

... I hope.

Author: oleibman

samples/templates/GnumericTest.gnumeric

@@ -2,6 +2,7 @@
 
 namespace PhpOffice\PhpSpreadsheet\Reader;
 
+use PhpOffice\PhpSpreadsheet\Reader\Exception as ReaderException;
 use PhpOffice\PhpSpreadsheet\Reader\Security\XmlScanner;
 use PhpOffice\PhpSpreadsheet\Shared\File;
 
@@ -133,11 +134,7 @@ public function setReadFilter(IReadFilter $pValue)
 
     public function getSecurityScanner()
     {
-        if (property_exists($this, 'securityScanner')) {
-            return $this->securityScanner;
-        }
-
-        return null;
+        return $this->securityScanner;
     }
 
     /**
@@ -147,12 +144,18 @@ public function getSecurityScanner()
      */
     protected function openFile($pFilename): void
     {
-        File::assertFile($pFilename);
+        if ($pFilename) {
+            File::assertFile($pFilename);
 
-        // Open file
-        $this->fileHandle = fopen($pFilename, 'rb');
-        if ($this->fileHandle === false) {
-            throw new Exception('Could not open file ' . $pFilename . ' for reading.');
+            // Open file
+            $fileHandle = fopen($pFilename, 'rb');
+        } else {
+            $fileHandle = false;
+        }
+        if ($fileHandle !== false) {
+            $this->fileHandle = $fileHandle;
+        } else {
+            throw new ReaderException('Could not open file ' . $pFilename . ' for reading.');
         }
     }
 }