Consistently use fseeko.
From BALATON Zoltan.
diff --git a/lib/zip_source_filep.c b/lib/zip_source_filep.c
index a57b0b6..4e51eb0 100644
--- a/lib/zip_source_filep.c
+++ b/lib/zip_source_filep.c
@@ -134,7 +134,7 @@
             ctx->supports = ZIP_SOURCE_SUPPORTS_WRITABLE;
 	}
     }
-    else if (fseek(ctx->f, 0, SEEK_CUR) == 0) {
+    else if (fseeko(ctx->f, 0, SEEK_CUR) == 0) {
         ctx->supports = ZIP_SOURCE_SUPPORTS_SEEKABLE;
     }