Fix weird gesture deactivation and state-save bug with weird fix.

Also OCDly replace a NULL with nullptr (not part of the above fix).

indra/newview/llgesturemgr.h

@@ -125,7 +125,7 @@ public:
 	bool triggerGesture(KEY key, MASK mask);
 
 	// Trigger all gestures referenced as substrings in this string
-	bool triggerAndReviseString(const std::string &str, std::string *revised_string = NULL);
+	bool triggerAndReviseString(const std::string &str, std::string *revised_string = nullptr);
 
 	// Does some gesture have this key bound?
 	//bool isKeyBound(KEY key, MASK mask) const;