Fix an edge case with GPS data handling that results in this error:

fread: Length parameter must be greater than 0 in file modules/exif/lib/makers/gps.php on line 197

Filed upstream as:
  http://www.zenphoto.org/trac/ticket/1108

1 files changed, 4 insertions, 0 deletions

diff --git a/modules/exif/lib/makers/gps.php b/modules/exif/lib/makers/gps.php
index 838c05a8..e520a1f7 100644
--- a/modules/exif/lib/makers/gps.php
+++ b/modules/exif/lib/makers/gps.php
@@ -195,6 +195,10 @@ function parseGPS($block,&$result,$offset,$seek, $globalOffset) {
 	$num=hexdec($num);
 	$result['GPS']['NumTags'] = $num;
 
+	if ($num == 0) {
+		return;
+	}
+
 	$block = fread( $seek, $num*12 );
 	$place = 0;