fixed the validation of sequences content model when some of the blocks

* xmlregexp.c xmlschemas.c: fixed the validation of sequences
  content model when some of the blocks have min or max, and a couple
  of bugs found in the process.
* result/schemas/list0* test/schemas/list0*: added some specific
  regression tests
Daniel
diff --git a/xmlregexp.c b/xmlregexp.c
index 627da51..155a2f0 100644
--- a/xmlregexp.c
+++ b/xmlregexp.c
@@ -2335,8 +2335,10 @@
     if (exec->inputStack != NULL) {
 	int i;
 
-	for (i = 0;i < exec->inputStackNr;i++)
-	    xmlFree(exec->inputStack[i].value);
+	for (i = 0;i < exec->inputStackNr;i++) {
+	    if (exec->inputStack[i].value != NULL)
+		xmlFree(exec->inputStack[i].value);
+	}
 	xmlFree(exec->inputStack);
     }
     xmlFree(exec);