Return empty array if no valid command detected

In some edge cases, the formatContent() method may return a document stream row containing an invalid command. Make sure we just ignore these commands instead of triggering warnings for missing $matches array elements.

src/Smalot/PdfParser/PDFObject.php

@@ -974,6 +974,11 @@ public function getCommandsText(string $text_part, int &$offset = 0): array
 
         preg_match('/^(([\/\[\(<])?.*)(?<!\w)([a-z01\'\"*]+)$/i', $text_part, $matches);
 
+        // If no valid command is detected, return an empty array
+        if (!isset($matches[1]) || !isset($matches[2]) || !isset($matches[3])) {
+            return [];
+        }
+
         $type = $matches[2];
         $operator = $matches[3];
         $command = trim($matches[1]);

tests/PHPUnit/Integration/PDFObjectTest.php

@@ -463,4 +463,23 @@ public function testFontIDWithHyphen(): void
         $this->assertEquals('Tf', $fontCommandHyphen[0]['o']);
         $this->assertEquals('FID-01 15.00', $fontCommandHyphen[0]['c']);
     }
+
+    /**
+     * Tests that an invalid command does not cause an error, but just
+     * returns an empty array
+     */
+    public function testInvalidCommand(): void
+    {
+        $pdfObject = $this->getPdfObjectInstance(new Document());
+
+        $validCommand = $pdfObject->getCommandsText('75 rg');
+
+        $this->assertEquals('', $validCommand[0]['t']);
+        $this->assertEquals('rg', $validCommand[0]['o']);
+        $this->assertEquals('75', $validCommand[0]['c']);
+
+        $invalidCommand = $pdfObject->getCommandsText('75');
+
+        $this->assertEquals([], $invalidCommand);
+    }
 }