Fix: ignore *pass-on* counters when detecting left-button grabs (#3990)

LLAgent::leftButtonGrabbed() must report TRUE only when an attachment has
**actually grabbed** the left mouse button (accept = TRUE, pass_on = FALSE), like every other ...Grabbed() function below it

Author: Sekkmer

indra/newview/llagent.cpp

@@ -3469,11 +3469,14 @@ void LLAgent::initOriginGlobal(const LLVector3d &origin_global)
 
 bool LLAgent::leftButtonGrabbed() const
 {
-    const bool camera_mouse_look = gAgentCamera.cameraMouselook();
-    return (!camera_mouse_look && mControlsTakenCount[CONTROL_LBUTTON_DOWN_INDEX] > 0)
-        || (camera_mouse_look && mControlsTakenCount[CONTROL_ML_LBUTTON_DOWN_INDEX] > 0)
-        || (!camera_mouse_look && mControlsTakenPassedOnCount[CONTROL_LBUTTON_DOWN_INDEX] > 0)
-        || (camera_mouse_look && mControlsTakenPassedOnCount[CONTROL_ML_LBUTTON_DOWN_INDEX] > 0);
+    if (gAgentCamera.cameraMouselook())
+    {
+        return mControlsTakenCount[CONTROL_ML_LBUTTON_DOWN_INDEX] > 0;
+    }
+    else
+    {
+        return mControlsTakenCount[CONTROL_LBUTTON_DOWN_INDEX] > 0;
+    }
 }
 
 bool LLAgent::rotateGrabbed() const