COMMON: SEEK_END offsets are negative

This was taken directly from the old code, which either used different
semantics, or had a genuine bug

1 files changed, 1 insertions, 1 deletions

diff --git a/common/zlib.cpp b/common/zlib.cpp
index 1c7e8437fe..f1a298a9f1 100644
--- a/common/zlib.cpp
+++ b/common/zlib.cpp
@@ -252,7 +252,7 @@ public:
 			break;
 		case SEEK_END:
 			// NOTE: This can be an expensive operation (see below).
-			newPos = size() - offset;
+			newPos = size() + offset;
 			break;
 		}