Fix memory leak in non-constant module declaration

tests/jq.test

@@ -1181,6 +1181,10 @@ include "c"; [a, c]
 null
 [0,"acmehbah"]
 
+%%FAIL
+module (.+1); 0
+jq: error: Module metadata must be constant at <top-level>, line 1:
+
 %%FAIL
 include "a" (.+1); 0
 jq: error: Module metadata must be constant at <top-level>, line 1: