Fix 5 issues reported by PVS studio

* src/sky.cpp  146     warn    V519 The 'suncolor_f.r' variable is assigned values twice successively. Perhaps this is a mistake. Check lines: 142, 146.
* src/sky.cpp  147     warn    V519 The 'suncolor_f.g' variable is assigned values twice successively. Perhaps this is a mistake. Check lines: 143, 147.
* src/sky.cpp  148     warn    V519 The 'suncolor_f.b' variable is assigned values twice successively. Perhaps this is a mistake. Check lines: 144, 148.
* src/threading/thread.cpp     63      err     V730 Not all members of a class are initialized inside the constructor. Consider inspecting: m_thread_obj.
* src/server.cpp       3243    err     V595 The 'log' pointer was utilized before it was verified against nullptr. Check lines: 3243, 3258.

src/server.cpp

@@ -3237,7 +3237,8 @@ bool Server::rollbackRevertActions(const std::list<RollbackAction> &actions,
 	ServerMap *map = (ServerMap*)(&m_env->getMap());
 
 	// Fail if no actions to handle
-	if(actions.empty()){
+	if (actions.empty()) {
+		assert(log);
 		log->push_back("Nothing to do.");
 		return false;
 	}

src/sky.cpp

@@ -141,9 +141,9 @@ void Sky::render()
 		suncolor_f.g = MYMAX(0.3, MYMIN(1.0, 0.7 + m_time_brightness * 0.5));
 		suncolor_f.b = MYMAX(0.0, m_brightness * 0.95);
 		video::SColorf suncolor2_f(1, 1, 1, 1);
-		suncolor_f.r = 1;
-		suncolor_f.g = MYMAX(0.3, MYMIN(1.0, 0.85 + m_time_brightness * 0.5));
-		suncolor_f.b = MYMAX(0.0, m_brightness);
+		suncolor2_f.r = 1;
+		suncolor2_f.g = MYMAX(0.3, MYMIN(1.0, 0.85 + m_time_brightness * 0.5));
+		suncolor2_f.b = MYMAX(0.0, m_brightness);
 
 		float moonsize = 0.04;
 		video::SColorf mooncolor_f(0.50, 0.57, 0.65, 1);

src/threading/thread.h

@@ -152,7 +152,7 @@ private:
 	std::mutex m_mutex;
 	std::mutex m_start_finished_mutex;
 
-	std::thread *m_thread_obj;
+	std::thread *m_thread_obj = nullptr;
 
 
 #ifdef _AIX