Scribe: fix handwriting is not initiated in WebView

View#getHandwritingArea mistakenly returned a non-null Rect even for
view's which never calls setHandwritingArea. As a result, handwriting
is not properly initation for views other than EditText.

Bug: 227278641
Test: atest android.view.inputmethod.cts.StylusHandwritingTest
Change-Id: I45700f2684a2f4138f73eaa843d3019e6c26d2f6