Fix a bug where nanos aren't unsummoned when unequipped.

Thanks fabriXfinn for reporting it.
Also improved sanity checks.

src/NanoManager.hpp

@@ -13,6 +13,7 @@ namespace NanoManager {
 
     // Helper methods
     void addNano(CNSocket* sock, int16_t nanoId, int16_t slot);
+    void summonNano(CNSocket* sock, int slot);
     void setNanoSkill(CNSocket* sock, int16_t nanoId, int16_t skillId);
     void resetNanoSkill(CNSocket* sock, int16_t nanoId);
 }