QCameraPrivate: NULL-fill fields to be set up by init().

c.f. the constructor already doing the same for provider and the
various fields populated by initControls(), which init() calls.
Should be redundant (all QCamera constructors do invoke d->init() as
soon as they've constructed d), but better safe than sorry.  Calms
Coverity (CID 22319).

Change-Id: Ibf5d13bb1ef17be8e66fa14ed5617b700051c495
Reviewed-by: Yoann Lopes <yoann.lopes@qt.io>

src/multimedia/camera/qcamera_p.h

@@ -72,6 +72,9 @@ public:
         infoControl(0),
         viewfinderSettingsControl(0),
         viewfinderSettingsControl2(0),
+        cameraExposure(0),
+        cameraFocus(0),
+        imageProcessing(0),
         viewfinder(0),
         capture(0),
         state(QCamera::UnloadedState),