Followup to IIS installer tweaks in [9bb48c36]:

* skip 0-byte config files when initializing, go ahead and redirect to installer if no non-0-byte files
* tweak warning on installer.php to let you know if you have a 0-byte config.php that's not writable, as opposed to generally already having a config.php with data in it

lib/installer.php

@@ -85,7 +85,11 @@ abstract class Installer
         $config = INSTALLDIR.'/config.php';
         if (file_exists($config)) {
             if (!is_writable($config) || filesize($config) > 0) {
-                $this->warning('Config file "config.php" already exists.');
+                if (filesize($config) == 0) {
+                    $this->warning('Config file "config.php" already exists and is empty, but is not writable.');
+                } else {
+                    $this->warning('Config file "config.php" already exists.');
+                }
                 $pass = false;
             }
         }

lib/statusnet.php

@@ -336,8 +336,11 @@ class StatusNet
 
         foreach ($config_files as $_config_file) {
             if (@file_exists($_config_file)) {
-                include($_config_file);
-                self::$have_config = true;
+                // Ignore 0-byte config files
+                if (filesize($_config_file) > 0) {
+                    include($_config_file);
+                    self::$have_config = true;
+                }
             }
         }