Fix oc-1163: gzdecode function not always defined

This function is only found in newer php versions

lib/minimizer.php

@@ -46,3 +46,13 @@ abstract class OC_Minimizer {
 		echo $out;
 	}
 }
+
+if (!function_exists('gzdecode')) {
+	function gzdecode($data,$maxlength=null,&$filename='',&$error='')
+	{
+		if (strcmp(substr($data,0,9),"\x1f\x8b\x8\0\0\0\0\0\0")) {
+			return null;  // Not the GZIP format we expect (See RFC 1952)
+		}
+		return gzinflate(substr($data,10,-8));
+	}
+}