getAppValue expects string

Co-authored-by: Pytal <24800714+Pytal@users.noreply.github.com>
Signed-off-by: John Molakvoæ <skjnldsv@users.noreply.github.com>

lib/private/legacy/OC_Image.php

@@ -415,7 +415,7 @@ class OC_Image implements \OCP\IImage {
 	 * @return int|null
 	 */
 	protected function getJpegQuality() {
-		$quality = $this->config->getAppValue('preview', 'jpeg_quality', 80);
+		$quality = $this->config->getAppValue('preview', 'jpeg_quality', '80');
 		if ($quality !== null) {
 			$quality = min(100, max(10, (int) $quality));
 		}

tests/lib/ImageTest.php

@@ -140,7 +140,7 @@ class ImageTest extends \Test\TestCase {
 		$config = $this->createMock(IConfig::class);
 		$config->expects($this->once())
 			->method('getAppValue')
-			->with('preview', 'jpeg_quality', 80)
+			->with('preview', 'jpeg_quality', '80')
 			->willReturn(null);
 		$config->expects($this->once())
 			->method('getSystemValueInt')