Avoid negative connection count on Sphinx restart

Difference calculation can go negative when Sphinx is restarted. This makes ugly spikes in the graph.

plugins/sphinx/sphinx_connections

@@ -54,6 +54,9 @@ if (!file_exists($sTmpFilePath)) {
     fclose($fp);
 
     $toShow = (int) ($iCurrent - (int) $iOldCount);
+    if ($toShow < 0) {
+      $toShow = 0;
+    }
 }
 
 echo "current.value $toShow\n";