Only remove the indexer lock when there is really a stale lock

Previously the rmdir could be executed when the lock directory had been
deleted by another indexer already. This could lead to a race condition
when another indexer call creates the lock again between the if and the
rmdir. This issue still exists for stale lock directories but they
normally shouldn't exist.
This also prevents the loop from becoming an endless loop when the lock
directory can't be created.
This change also fixes a syntax error in the indexer and prevents an
endless loop when the lock directory exists but can't be deleted.

lib/exe/indexer.php

@@ -153,11 +153,15 @@ function runIndexer(){
     $lock = $conf['lockdir'].'/_indexer.lock';
     while(!@mkdir($lock,$conf['dmode'])){
         usleep(50);
-        if(time()-@filemtime($lock) > 60*5){
+        if(is_dir($lock) && time()-@filemtime($lock) > 60*5){
             // looks like a stale lock - remove it
-            @rmdir($lock);
-            print "runIndexer(): stale lock removed".NL;
-        }elseif($run++ = 1000){
+            if (!@rmdir($lock)) {
+                print "runIndexer(): removing the stale lock failed".NL;
+                return false;
+            } else {
+                print "runIndexer(): stale lock removed".NL;
+            }
+        }elseif($run++ == 1000){
             // we waited 5 seconds for that lock
             print "runIndexer(): indexer locked".NL;
             return false;