fix for thumbnailer command line argument handler

docs/changelog/7.x.x.txt

@@ -5,6 +5,7 @@
    Technologies)
  - fix: Bug in thumbnailer.pl
  - fix: Events userDefined fields now work.
+ - fix: Bug in thumbnailer.pl revisited ("guiuser")
 
 
 7.3.12

sbin/thumbnailer.pl

@@ -33,7 +33,7 @@ my $ok = GetOptions(
 	'path=s'=>\$path
 );
 
-if ($help || ($path && $ok) ) {
+if ($help || !($path && $ok) ) {
   print <<USAGE;
 Usage: perl $0 --path=/path/to/files [--size=thumbnailSize] [--missing]