[doc] mod_fastcgi: extend php fastcgi example with physical file test

Change-Id: I061278e2bd588d27f57be8b6711d470161a955cc

doc/mod_fastcgi.xml

@@ -28,7 +28,7 @@
 					module_load "mod_fastcgi";
 				}
 
-				if phys.path =$ ".php" {
+				if phys.path =$ ".php" and phys.is_file {
 					fastcgi "unix:/var/run/lighttpd2/php.sock";
 				}
 			</config>