Remove check for za == NULL (which would segfault while setting the error).

--HG--
branch : HEAD
diff --git a/lib/zip_source_crc.c b/lib/zip_source_crc.c
index 7ffbfea..59e8a19 100644
--- a/lib/zip_source_crc.c
+++ b/lib/zip_source_crc.c
@@ -56,7 +56,7 @@
 {
     struct crc *ctx;
 
-    if (za == NULL || src == NULL) {
+    if (src == NULL) {
 	_zip_error_set(&za->error, ZIP_ER_INVAL, 0);
 	return NULL;
     }