Initialize mCurrentPageCanvas on construction

This was our only field member that wasn't implicitly or explicitly
initialized on construction.  nullptr is a known state for this
value, and so we initialize it to nullptr.

Bug: 176903027
Test: TreeHugger
Change-Id: Ief600d1ab7c8f34dac91f7bf9f494e05bb61e3b3
diff --git a/libs/renderengine/skia/debug/SkiaCapture.h b/libs/renderengine/skia/debug/SkiaCapture.h
index 08a1359..5e18e60 100644
--- a/libs/renderengine/skia/debug/SkiaCapture.h
+++ b/libs/renderengine/skia/debug/SkiaCapture.h
@@ -75,7 +75,7 @@
     std::unique_ptr<SkSharingSerialContext> mSerialContext;
     std::unique_ptr<SkNWayCanvas> mNwayCanvas;
 
-    SkCanvas* mCurrentPageCanvas;
+    SkCanvas* mCurrentPageCanvas = nullptr;
 
     // Capturing and interval control.
     bool mCaptureRunning = false;