Trace view: Fix tooltip "Illegal Argument Exception"

Fix the corner case where resizing and rendering are not synchronized (e.g., when resizing is faster than rendering). The impact of this issue is that the coordinate X and/or Y can be zero or bigger than the size of the canvas. This causes an illegal argument exception when calling imageData.getPixel(x, y)

Signed-off-by: Laksono Adhianto laksono@gmail.com