AdminerDarkSwitcher: Handle first click

Fixed an issue where the Dark Mode Switcher icon did not respond on the first click if the Dark Mode cookie had not been set yet. Now, clicking the icon correctly sets the cookie and immediately toggles Dark Mode.

plugins/dark-switcher.php

@@ -28,6 +28,8 @@ const saved = document.cookie.match(/adminer_dark=(\d)/);
 if (saved) {
 	adminerDark = +saved[1];
 	adminerDarkSet();
+} else {
+	adminerDark = +matchMedia('(prefers-color-scheme: dark)').matches;
 }
 </script>
 <?php
@@ -35,7 +37,7 @@ if (saved) {
 
 	function navigation($missing) {
 		echo "<big style='position: fixed; bottom: .5em; right: .5em; cursor: pointer;'>☀</big>"
-			. Adminer\script("if (adminerDark != null) adminerDarkSet(); qsl('big').onclick = adminerDarkSwitch;") . "\n"
+			. Adminer\script("adminerDarkSet(); qsl('big').onclick = adminerDarkSwitch;") . "\n"
 		;
 	}