UWP: Simplify QueryPerformanceCounter usage

platform/uwp/os_uwp.cpp

@@ -136,12 +136,8 @@ void OS_UWP::initialize_core() {
 	NetSocketPosix::make_default();
 
 	// We need to know how often the clock is updated
-	if (!QueryPerformanceFrequency((LARGE_INTEGER *)&ticks_per_second))
-		ticks_per_second = 1000;
-	// If timeAtGameStart is 0 then we get the time since
-	// the start of the computer when we call GetGameTime()
-	ticks_start = 0;
-	ticks_start = get_ticks_usec();
+	QueryPerformanceFrequency((LARGE_INTEGER *)&ticks_per_second);
+	QueryPerformanceCounter((LARGE_INTEGER *)&ticks_start);
 
 	IPUnix::make_default();
 
@@ -525,6 +521,9 @@ uint64_t OS_UWP::get_ticks_usec() const {
 
 	// This is the number of clock ticks since start
 	QueryPerformanceCounter((LARGE_INTEGER *)&ticks);
+	// Subtract the ticks at game start to get
+	// the ticks since the game started
+	ticks -= ticks_start;
 
 	// Divide by frequency to get the time in seconds
 	// original calculation shown below is subject to overflow
@@ -544,9 +543,6 @@ uint64_t OS_UWP::get_ticks_usec() const {
 	// seconds
 	time += seconds * 1000000L;
 
-	// Subtract the time at game start to get
-	// the time since the game started
-	time -= ticks_start;
 	return time;
 }