removed some surplus null appends that got typoed in 0e29f7974b59e4440cf02e1388fb9d8ab2b5c5fd

A couple of null appends got typoed to append a '0' character instead.
Removed them here since String already takes care of the null terminator for us.

core/os/file_access.cpp

@@ -270,7 +270,6 @@ String FileAccess::get_token() const {
 		c = get_8();
 	}
 
-	token += '0';
 	return String::utf8(token.get_data());
 }
 

core/ustring.cpp

@@ -3881,8 +3881,6 @@ String String::percent_decode() const {
 		pe += c;
 	}
 
-	pe += '0';
-
 	return String::utf8(pe.ptr());
 }
 

editor/project_manager.cpp

@@ -1782,7 +1782,6 @@ ProjectManager::ProjectManager() {
 
 	String cp;
 	cp += 0xA9;
-	cp += '0';
 	OS::get_singleton()->set_window_title(VERSION_NAME + String(" - ") + TTR("Project Manager") + " - " + cp + " 2007-2018 Juan Linietsky, Ariel Manzur & Godot Contributors");
 
 	HBoxContainer *top_hb = memnew(HBoxContainer);