still more PR #1364

Earlier commit left out an intended line, resulting in the sanity
check being bogus because the incomplete test wasn't impossible.

src/version.c

@@ -364,6 +364,7 @@ check_version(
 {
     if (!filename) {
 #ifdef EXTRA_SANITY_CHECKS
+        if (complain)
             impossible("check_version() called with"
                        " 'complain'=True but 'filename'=Null");
 #endif