Also pass down "unknown" options to the converters from the stack con…

…verter. Fixes #259

src/Convert/Converters/Stack.php

@@ -134,8 +134,12 @@ protected function doActualConvert()
         $defaultConverterOptions = [];
 
         foreach ($this->options2->getOptionsMap() as $id => $option) {
-            if ($option->isValueExplicitlySet() && !($option instanceof GhostOption)) {
-                //$this->logLn('hi' . $id);
+            // Right here, there used to be a check that ensured that unknown options was not passed down to the
+            // converters (" && !($option instanceof GhostOption)"). But well, as the Stack doesn't know about
+            // converter specific options, such as "try-cwebp", these was not passed down (see #259)
+            // I'm not sure why the check was made in the first place, but it does not seem neccessary, as the
+            // converters simply ignore unknown options. So the check has now been removed.
+            if ($option->isValueExplicitlySet()) {
                 $defaultConverterOptions[$id] = $option->getValue();
             }
         }