[SignaturePad] Call Invalidate on canvasView directly (fixes #52509)
[SignaturePad] Call Invalidate on canvasView directly (fixes #52509)

On Android > 4.0, this causes the pad to show no feedback:

#5209
"The sample comes set for API Level 8 ..and appears to work great.

However, I am building for API Level 15 ...when capturing a signature
there
is no visible feedback..once you stop a particular part of the
signature the
component will then immediately show what was captured. When I switch
the
sample to API Level 15 I am able to recreate the problem I am seeing in
my
application."

xamarin/SignaturePad,xamarin/SignaturePad