BGE: Fix T45945: Action bouncing.

Bug introduced in 583fa7d1e, KX_GameObject.setActionFrame can make BL_Action::m_starttime negative. But in BL_Action::Update m_starttime is set to the current time if it's negative.
To fix it we use a boolean BL_Action::m_initializedTime to know if we should initialize the time in BL_Action::Update, it's more stable than comparing times.

Tested with bug task T45945 and T32054, with an extra patch about to fix suspend resume scene issues with actions : D1569

source/gameengine/Ketsji/BL_Action.cpp

@@ -84,7 +84,8 @@ BL_Action::BL_Action(class KX_GameObject* gameobj)
 	m_blendmode(ACT_BLEND_BLEND),
 	m_ipo_flags(0),
 	m_done(true),
-	m_calc_localtime(true)
+	m_calc_localtime(true),
+	m_initializedTime(false)
 {
 }
 
@@ -271,6 +272,7 @@ bool BL_Action::Play(const char* name,
 	m_layer_weight = layer_weight;
 	
 	m_done = false;
+	m_initializedTime = false;
 
 	return true;
 }
@@ -400,8 +402,10 @@ void BL_Action::Update(float curtime)
 
 	// Grab the start time here so we don't end up with a negative m_localframe when
 	// suspending and resuming scenes.
-	if (m_starttime < 0)
+	if (!m_initializedTime) {
 		m_starttime = curtime;
+		m_initializedTime = true;
+	}
 
 	if (m_calc_localtime)
 		SetLocalTime(curtime);

source/gameengine/Ketsji/BL_Action.h

@@ -69,6 +69,8 @@ private:
 
 	bool m_done;
 	bool m_calc_localtime;
+	/// Set to true when m_starttime is initialized in Update.
+	bool m_initializedTime;
 
 	void ClearControllerList();
 	void InitIPO();