*Fix the bug that knockback cause client crash.

--HG--
branch : trunk

src/game/SpellEffects.cpp

@@ -5935,7 +5935,7 @@ void Spell::EffectKnockBack(uint32 i)
         return;
 
     float x, y;
-    if(m_targets.HasDest())
+    if(m_targets.m_targetMask & TARGET_FLAG_DEST_LOCATION)
     {
         x = m_targets.m_destX;
         y = m_targets.m_destY;
@@ -5948,10 +5948,19 @@ void Spell::EffectKnockBack(uint32 i)
 
     float dx = unitTarget->GetPositionX() - x;
     float dy = unitTarget->GetPositionY() - y;
-    float dist = sqrt((dx*dx) + (dy*dy));
-
-    float vcos = dx / dist;
-    float vsin = dy / dist;
+    float vcos, vsin;
+    if(dx < 0.001f && dy < 0.001f)
+    {
+        float angle = rand_norm()*2*M_PI;
+        vcos = cos(angle);
+        vsin = sin(angle);
+    }
+    else
+    {
+        float dist = sqrt((dx*dx) + (dy*dy));
+        vcos = dx / dist;
+        vsin = dy / dist;
+    }
 
     WorldPacket data(SMSG_MOVE_KNOCK_BACK, (8+4+4+4+4+4));
     data.append(unitTarget->GetPackGUID());