fixup! miniscript: check maximum stack size during execution

src/script/miniscript.h

@@ -1457,16 +1457,21 @@ struct Node {
         return true;
     }
 
+    /** Whether this node is of type B, K or W. (That is, anything but V.) */
+    bool IsBKW() const {
+        return !((GetType() & "BKW"_mst) == ""_mst);
+    }
+
     /** Return the maximum number of stack elements needed to satisfy this script non-malleably. */
     std::optional<uint32_t> GetStackSize() const {
         if (!ss.sat.valid) return {};
-        return ss.sat.netdiff + 1;
+        return ss.sat.netdiff + static_cast<int32_t>(IsBKW());
     }
 
     //! Return the maximum size of the stack during execution of this script.
     std::optional<uint32_t> GetExecStackSize() const {
         if (!ss.sat.valid) return {};
-        return ss.sat.exec + 1;
+        return ss.sat.exec + static_cast<int32_t>(IsBKW());
     }
 
     //! Check the maximum stack size for this script against the policy limit.