Fix possible path existence disclossure

On non released versions (where line counts are not precalculated) it
was possible to check for file existence due to limited checks for
supplied path.

Signed-off-by: Michal Čihař <michal@cihar.com>

libraries/error_report.lib.php

@@ -238,7 +238,7 @@ function PMA_countLines($filename)
     foreach (explode('/', $filename) as $part) {
         if ($part == '..') {
             $depath--;
-        } elseif ($part != '.') {
+        } elseif ($part != '.' || $part === '') {
             $depath++;
         }
         if ($depath < 0) {