php 8+ edge cases fixes (#630)

Co-authored-by: Nicola Asuni <nicolaasuni@users.noreply.github.com>

include/tcpdf_static.php

@@ -1780,7 +1780,7 @@ public static function pregSplit($pattern, $modifiers, $subject, $limit=NULL, $f
 			if ($ret === false) {
 				return array();
 			}
-			return $ret;
+			return is_array($ret) ? $ret : array();
 		}
 		// preg_split is bugged - try alternative solution
 		$ret = array();
@@ -2124,7 +2124,7 @@ public static function _freadint($f) {
 	 * Array of page formats
 	 * measures are calculated in this way: (inches * 72) or (millimeters * 72 / 25.4)
 	 * @public static
-	 * 
+	 *
      * @var array<string,float[]>
 	 */
 	public static $page_formats = array(

tcpdf.php

@@ -6409,7 +6409,7 @@ public function Write($h, $txt, $link='', $fill=false, $align='', $ln=false, $st
 		// calculate maximum width for a single character on string
 		$chrw = $this->GetArrStringWidth($chars, '', '', 0, true);
 		array_walk($chrw, array($this, 'getRawCharWidth'));
-		$maxchwidth = max($chrw);
+		$maxchwidth = ((is_array($chrw) || $chrw instanceof Countable) && count($chrw) > 0) ? max($chrw) : 0;
 		// get array of chars
 		$uchars = TCPDF_FONTS::UTF8ArrayToUniArray($chars, $this->isunicode);
 		// get the number of characters
@@ -6872,6 +6872,8 @@ protected function fitBlock($w, $h, $x, $y, $fitonpage=false) {
 		}
 		// resize the block to be contained on the remaining available page or column space
 		if ($fitonpage) {
+			// fallback to avoid division by zero
+			$h = $h == 0 ? 1 : $h;
 			$ratio_wh = ($w / $h);
 			if (($y + $h) > $this->PageBreakTrigger) {
 				$h = $this->PageBreakTrigger - $y;